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Ganeti walk-through
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===================
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Documents Ganeti version |version|
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.. contents::
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.. highlight:: text
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Introduction
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------------
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This document serves as a more example-oriented guide to Ganeti; while
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the administration guide shows a conceptual approach, here you will find
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a step-by-step example to managing instances and the cluster.
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Our simulated, example cluster will have three machines, named
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``node1``, ``node2``, ``node3``. Note that in real life machines will
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usually FQDNs but here we use short names for brevity. We will use a
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secondary network for replication data, ``192.168.2.0/24``, with nodes
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having the last octet the same as their index. The cluster name will be
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``example-cluster``. All nodes have the same simulated hardware
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configuration, two disks of 750GB, 32GB of memory and 4 CPUs.
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On this cluster, we will create up to seven instances, named
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``instance1`` to ``instance7``.
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Cluster creation
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----------------
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Follow the :doc:`install` document and prepare the nodes. Then it's time
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to initialise the cluster::
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  node1# gnt-cluster init -s 192.168.2.1 --enabled-hypervisors=xen-pvm cluster
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  node1#
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The creation was fine. Let's check that one node we have is functioning
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correctly::
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  node1# gnt-node list
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  Node  DTotal DFree MTotal MNode MFree Pinst Sinst
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  node1   1.3T  1.3T  32.0G  1.0G 30.5G     0     0
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  node1# gnt-cluster verify
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  Mon Oct 26 02:08:51 2009 * Verifying global settings
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  Mon Oct 26 02:08:51 2009 * Gathering data (1 nodes)
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  Mon Oct 26 02:08:52 2009 * Verifying node status
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  Mon Oct 26 02:08:52 2009 * Verifying instance status
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  Mon Oct 26 02:08:52 2009 * Verifying orphan volumes
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  Mon Oct 26 02:08:52 2009 * Verifying remaining instances
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  Mon Oct 26 02:08:52 2009 * Verifying N+1 Memory redundancy
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  Mon Oct 26 02:08:52 2009 * Other Notes
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  Mon Oct 26 02:08:52 2009 * Hooks Results
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  node1#
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Since this proceeded correctly, let's add the other two nodes::
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  node1# gnt-node add -s 192.168.2.2 node2
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  -- WARNING --
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  Performing this operation is going to replace the ssh daemon keypair
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  on the target machine (node2) with the ones of the current one
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  and grant full intra-cluster ssh root access to/from it
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  The authenticity of host 'node2 (192.168.1.2)' can't be established.
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  RSA key fingerprint is 9f:…
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  Are you sure you want to continue connecting (yes/no)? yes
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  root@node2's password:
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  Mon Oct 26 02:11:54 2009  - INFO: Node will be a master candidate
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  node1# gnt-node add -s 192.168.2.3 node3
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  -- WARNING --
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  Performing this operation is going to replace the ssh daemon keypair
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  on the target machine (node2) with the ones of the current one
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  and grant full intra-cluster ssh root access to/from it
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  The authenticity of host 'node3 (192.168.1.3)' can't be established.
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  RSA key fingerprint is 9f:…
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  Are you sure you want to continue connecting (yes/no)? yes
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  root@node2's password:
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  Mon Oct 26 02:11:54 2009  - INFO: Node will be a master candidate
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Checking the cluster status again::
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  node1# gnt-node list
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  Node  DTotal DFree MTotal MNode MFree Pinst Sinst
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  node1   1.3T  1.3T  32.0G  1.0G 30.5G     0     0
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  node2   1.3T  1.3T  32.0G  1.0G 30.5G     0     0
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  node3   1.3T  1.3T  32.0G  1.0G 30.5G     0     0
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  node1# gnt-cluster verify
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  Mon Oct 26 02:15:14 2009 * Verifying global settings
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  Mon Oct 26 02:15:14 2009 * Gathering data (3 nodes)
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  Mon Oct 26 02:15:16 2009 * Verifying node status
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  Mon Oct 26 02:15:16 2009 * Verifying instance status
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  Mon Oct 26 02:15:16 2009 * Verifying orphan volumes
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  Mon Oct 26 02:15:16 2009 * Verifying remaining instances
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  Mon Oct 26 02:15:16 2009 * Verifying N+1 Memory redundancy
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  Mon Oct 26 02:15:16 2009 * Other Notes
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  Mon Oct 26 02:15:16 2009 * Hooks Results
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  node1#
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And let's check that we have a valid OS::
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  node1# gnt-os list
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  Name
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  debootstrap
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  node1#
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Running a burnin
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----------------
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Now that the cluster is created, it is time to check that the hardware
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works correctly, that the hypervisor can actually create instances,
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etc. This is done via the debootstrap tool as described in the admin
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guide. Similar output lines are replaced with ``…`` in the below log::
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  node1# /usr/lib/ganeti/tools/burnin -o debootstrap -p instance{1..5}
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  - Testing global parameters
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  - Creating instances
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    * instance instance1
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      on node1, node2
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    * instance instance2
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      on node2, node3
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    * instance instance5
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      on node2, node3
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    * Submitted job ID(s) 157, 158, 159, 160, 161
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      waiting for job 157 for instance1
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      waiting for job 161 for instance5
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  - Replacing disks on the same nodes
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    * instance instance1
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      run replace_on_secondary
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      run replace_on_primary
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    * instance instance5
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      run replace_on_secondary
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      run replace_on_primary
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    * Submitted job ID(s) 162, 163, 164, 165, 166
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      waiting for job 162 for instance1
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  - Changing the secondary node
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    * instance instance1
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      run replace_new_secondary node3
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    * instance instance2
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      run replace_new_secondary node1
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    * instance instance5
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      run replace_new_secondary node1
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    * Submitted job ID(s) 167, 168, 169, 170, 171
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      waiting for job 167 for instance1
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  - Growing disks
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    * instance instance1
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      increase disk/0 by 128 MB
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    * instance instance5
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      increase disk/0 by 128 MB
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    * Submitted job ID(s) 173, 174, 175, 176, 177
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      waiting for job 173 for instance1
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  - Failing over instances
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    * instance instance1
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    * instance instance5
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    * Submitted job ID(s) 179, 180, 181, 182, 183
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      waiting for job 179 for instance1
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  - Migrating instances
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    * instance instance1
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      migration and migration cleanup
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    * instance instance5
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      migration and migration cleanup
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    * Submitted job ID(s) 184, 185, 186, 187, 188
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      waiting for job 184 for instance1
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  - Exporting and re-importing instances
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    * instance instance1
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      export to node node3
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      remove instance
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      import from node3 to node1, node2
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      remove export
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    * instance instance5
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      export to node node1
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      remove instance
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      import from node1 to node2, node3
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      remove export
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    * Submitted job ID(s) 196, 197, 198, 199, 200
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      waiting for job 196 for instance1
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  - Reinstalling instances
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    * instance instance1
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      reinstall without passing the OS
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      reinstall specifying the OS
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    * instance instance5
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      reinstall without passing the OS
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      reinstall specifying the OS
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    * Submitted job ID(s) 203, 204, 205, 206, 207
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      waiting for job 203 for instance1
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  - Rebooting instances
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    * instance instance1
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      reboot with type 'hard'
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      reboot with type 'soft'
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      reboot with type 'full'
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    * instance instance5
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      reboot with type 'hard'
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      reboot with type 'soft'
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      reboot with type 'full'
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    * Submitted job ID(s) 208, 209, 210, 211, 212
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      waiting for job 208 for instance1
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  - Adding and removing disks
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    * instance instance1
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      adding a disk
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      removing last disk
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    * instance instance5
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      adding a disk
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      removing last disk
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    * Submitted job ID(s) 213, 214, 215, 216, 217
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      waiting for job 213 for instance1
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  - Adding and removing NICs
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    * instance instance1
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      adding a NIC
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      removing last NIC
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    * instance instance5
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      adding a NIC
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      removing last NIC
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    * Submitted job ID(s) 218, 219, 220, 221, 222
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      waiting for job 218 for instance1
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  - Activating/deactivating disks
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    * instance instance1
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      activate disks when online
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      activate disks when offline
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      deactivate disks (when offline)
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    * instance instance5
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      activate disks when online
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      activate disks when offline
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      deactivate disks (when offline)
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    * Submitted job ID(s) 223, 224, 225, 226, 227
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      waiting for job 223 for instance1
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  - Stopping and starting instances
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    * instance instance1
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    * instance instance5
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    * Submitted job ID(s) 230, 231, 232, 233, 234
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      waiting for job 230 for instance1
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  - Removing instances
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    * instance instance1
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    * instance instance5
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    * Submitted job ID(s) 235, 236, 237, 238, 239
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      waiting for job 235 for instance1
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  node1#
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You can see in the above what operations the burnin does. Ideally, the
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burnin log would proceed successfully through all the steps and end
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cleanly, without throwing errors.
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Instance operations
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-------------------
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Creation
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++++++++
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At this point, Ganeti and the hardware seems to be functioning
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correctly, so we'll follow up with creating the instances manually::
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  node1# gnt-instance add -t drbd -o debootstrap -s 256m -n node1:node2 instance3
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  Mon Oct 26 04:06:52 2009  - INFO: Selected nodes for instance instance1 via iallocator hail: node2, node3
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  Mon Oct 26 04:06:53 2009 * creating instance disks...
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  Mon Oct 26 04:06:57 2009 adding instance instance1 to cluster config
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  Mon Oct 26 04:06:57 2009  - INFO: Waiting for instance instance1 to sync disks.
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  Mon Oct 26 04:06:57 2009  - INFO: - device disk/0: 20.00% done, 4 estimated seconds remaining
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  Mon Oct 26 04:07:01 2009  - INFO: Instance instance1's disks are in sync.
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  Mon Oct 26 04:07:01 2009 creating os for instance instance1 on node node2
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  Mon Oct 26 04:07:01 2009 * running the instance OS create scripts...
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  Mon Oct 26 04:07:14 2009 * starting instance...
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  node1# gnt-instance add -t drbd -o debootstrap -s 256m -n node1:node2 instanc<drbd -o debootstrap -s 256m -n node1:node2 instance2
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  Mon Oct 26 04:11:37 2009 * creating instance disks...
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  Mon Oct 26 04:11:40 2009 adding instance instance2 to cluster config
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  Mon Oct 26 04:11:41 2009  - INFO: Waiting for instance instance2 to sync disks.
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  Mon Oct 26 04:11:41 2009  - INFO: - device disk/0: 35.40% done, 1 estimated seconds remaining
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  Mon Oct 26 04:11:42 2009  - INFO: - device disk/0: 58.50% done, 1 estimated seconds remaining
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  Mon Oct 26 04:11:43 2009  - INFO: - device disk/0: 86.20% done, 0 estimated seconds remaining
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  Mon Oct 26 04:11:44 2009  - INFO: - device disk/0: 92.40% done, 0 estimated seconds remaining
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  Mon Oct 26 04:11:44 2009  - INFO: - device disk/0: 97.00% done, 0 estimated seconds remaining
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  Mon Oct 26 04:11:44 2009  - INFO: Instance instance2's disks are in sync.
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  Mon Oct 26 04:11:44 2009 creating os for instance instance2 on node node1
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  Mon Oct 26 04:11:44 2009 * running the instance OS create scripts...
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  Mon Oct 26 04:11:57 2009 * starting instance...
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  node1#
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The above shows one instance created via an iallocator script, and one
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being created with manual node assignment. The other three instances
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were also created and now it's time to check them::
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  node1# gnt-instance list
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  Instance  Hypervisor OS          Primary_node Status  Memory
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  instance1 xen-pvm    debootstrap node2        running   128M
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  instance2 xen-pvm    debootstrap node1        running   128M
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  instance3 xen-pvm    debootstrap node1        running   128M
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  instance4 xen-pvm    debootstrap node3        running   128M
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  instance5 xen-pvm    debootstrap node2        running   128M
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Accessing instances
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+++++++++++++++++++
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Accessing an instance's console is easy::
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  node1# gnt-instance console instance2
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  [    0.000000] Bootdata ok (command line is root=/dev/sda1 ro)
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  [    0.000000] Linux version 2.6…
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  [    0.000000] BIOS-provided physical RAM map:
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  [    0.000000]  Xen: 0000000000000000 - 0000000008800000 (usable)
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  [13138176.018071] Built 1 zonelists.  Total pages: 34816
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  [13138176.018074] Kernel command line: root=/dev/sda1 ro
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  [13138176.018694] Initializing CPU#0
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  Checking file systems...fsck 1.41.3 (12-Oct-2008)
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  done.
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  Setting kernel variables (/etc/sysctl.conf)...done.
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  Mounting local filesystems...done.
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  Activating swapfile swap...done.
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  Setting up networking....
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  Configuring network interfaces...done.
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  Setting console screen modes and fonts.
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  INIT: Entering runlevel: 2
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  Starting enhanced syslogd: rsyslogd.
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  Starting periodic command scheduler: crond.
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  Debian GNU/Linux 5.0 instance2 tty1
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  instance2 login:
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At this moment you can login to the instance and, after configuring the
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network (and doing this on all instances), we can check their
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connectivity::
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  node1# fping instance{1..5}
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  instance1 is alive
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  instance2 is alive
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  instance3 is alive
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  instance4 is alive
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  instance5 is alive
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  node1#
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Removal
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+++++++
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Removing unwanted instances is also easy::
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  node1# gnt-instance remove instance5
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  This will remove the volumes of the instance instance5 (including
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  mirrors), thus removing all the data of the instance. Continue?
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  y/[n]/?: y
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  node1#
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Recovering from hardware failures
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---------------------------------
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Recovering from node failure
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++++++++++++++++++++++++++++
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We are now left with four instances. Assume that at this point, node3,
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which has one primary and one secondary instance, crashes::
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  node1# gnt-node info node3
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  Node name: node3
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    primary ip: 172.24.227.1
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    secondary ip: 192.168.2.3
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    master candidate: True
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    drained: False
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    offline: False
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    primary for instances:
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      - instance4
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    secondary for instances:
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      - instance1
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  node1# fping node3
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  node3 is unreachable
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At this point, the primary instance of that node (instance4) is down,
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but the secondary instance (instance1) is not affected except it has
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lost disk redundancy::
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  node1# fping instance{1,4}
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  instance1 is alive
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  instance4 is unreachable
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  node1#
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If we try to check the status of instance4 via the instance info
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command, it fails because it tries to contact node3 which is down::
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  node1# gnt-instance info instance4
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  Failure: command execution error:
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  Error checking node node3: Connection failed (113: No route to host)
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  node1#
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So we need to mark node3 as being *offline*, and thus Ganeti won't talk
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to it anymore::
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  node1# gnt-node modify -O yes -f node3
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  Mon Oct 26 04:34:12 2009  - WARNING: Not enough master candidates (desired 10, new value will be 2)
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  Mon Oct 26 04:34:15 2009  - WARNING: Communication failure to node node3: Connection failed (113: No route to host)
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  Modified node node3
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   - offline -> True
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   - master_candidate -> auto-demotion due to offline
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  node1#
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And now we can failover the instance::
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  node1# gnt-instance failover --ignore-consistency instance4
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  Failover will happen to image instance4. This requires a shutdown of
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  the instance. Continue?
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  y/[n]/?: y
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  Mon Oct 26 04:35:34 2009 * checking disk consistency between source and target
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  Failure: command execution error:
429
  Disk disk/0 is degraded on target node, aborting failover.
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  node1# gnt-instance failover --ignore-consistency instance4
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  Failover will happen to image instance4. This requires a shutdown of
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  the instance. Continue?
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  y/[n]/?: y
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  Mon Oct 26 04:35:47 2009 * checking disk consistency between source and target
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  Mon Oct 26 04:35:47 2009 * shutting down instance on source node
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  Mon Oct 26 04:35:47 2009  - WARNING: Could not shutdown instance instance4 on node node3. Proceeding anyway. Please make sure node node3 is down. Error details: Node is marked offline
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  Mon Oct 26 04:35:47 2009 * deactivating the instance's disks on source node
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  Mon Oct 26 04:35:47 2009  - WARNING: Could not shutdown block device disk/0 on node node3: Node is marked offline
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  Mon Oct 26 04:35:47 2009 * activating the instance's disks on target node
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  Mon Oct 26 04:35:47 2009  - WARNING: Could not prepare block device disk/0 on node node3 (is_primary=False, pass=1): Node is marked offline
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  Mon Oct 26 04:35:48 2009 * starting the instance on the target node
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  node1#
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Note in our first attempt, Ganeti refused to do the failover since it
445
wasn't sure what is the status of the instance's disks. We pass the
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``--ignore-consistency`` flag and then we can failover::
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448
  node1# gnt-instance list
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  Instance  Hypervisor OS          Primary_node Status  Memory
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  instance1 xen-pvm    debootstrap node2        running   128M
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  instance2 xen-pvm    debootstrap node1        running   128M
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  instance3 xen-pvm    debootstrap node1        running   128M
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  instance4 xen-pvm    debootstrap node1        running   128M
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  node1#
455

    
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But at this point, both instance1 and instance4 are without disk
457
redundancy::
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459
  node1# gnt-instance info instance1
460
  Instance name: instance1
461
  UUID: 45173e82-d1fa-417c-8758-7d582ab7eef4
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  Serial number: 2
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  Creation time: 2009-10-26 04:06:57
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  Modification time: 2009-10-26 04:07:14
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  State: configured to be up, actual state is up
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    Nodes:
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      - primary: node2
468
      - secondaries: node3
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    Operating system: debootstrap
470
    Allocated network port: None
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    Hypervisor: xen-pvm
472
      - root_path: default (/dev/sda1)
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      - kernel_args: default (ro)
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      - use_bootloader: default (False)
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      - bootloader_args: default ()
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      - bootloader_path: default ()
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      - kernel_path: default (/boot/vmlinuz-2.6-xenU)
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      - initrd_path: default ()
479
    Hardware:
480
      - VCPUs: 1
481
      - memory: 128MiB
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      - NICs:
483
        - nic/0: MAC: aa:00:00:78:da:63, IP: None, mode: bridged, link: xen-br0
484
    Disks:
485
      - disk/0: drbd8, size 256M
486
        access mode: rw
487
        nodeA:       node2, minor=0
488
        nodeB:       node3, minor=0
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        port:        11035
490
        auth key:    8e950e3cec6854b0181fbc3a6058657701f2d458
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        on primary:  /dev/drbd0 (147:0) in sync, status *DEGRADED*
492
        child devices:
493
          - child 0: lvm, size 256M
494
            logical_id: xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_data
495
            on primary: /dev/xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_data (254:0)
496
          - child 1: lvm, size 128M
497
            logical_id: xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta
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            on primary: /dev/xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta (254:1)
499

    
500
The output is similar for instance4. In order to recover this, we need
501
to run the node evacuate command which will change from the current
502
secondary node to a new one (in this case, we only have two working
503
nodes, so all instances will be end on nodes one and two)::
504

    
505
  node1# gnt-node evacuate -I hail node3
506
  Relocate instance(s) 'instance1','instance4' from node
507
   node3 using iallocator hail?
508
  y/[n]/?: y
509
  Mon Oct 26 05:05:39 2009  - INFO: Selected new secondary for instance 'instance1': node1
510
  Mon Oct 26 05:05:40 2009  - INFO: Selected new secondary for instance 'instance4': node2
511
  Mon Oct 26 05:05:40 2009 Replacing disk(s) 0 for instance1
512
  Mon Oct 26 05:05:40 2009 STEP 1/6 Check device existence
513
  Mon Oct 26 05:05:40 2009  - INFO: Checking disk/0 on node2
514
  Mon Oct 26 05:05:40 2009  - INFO: Checking volume groups
515
  Mon Oct 26 05:05:40 2009 STEP 2/6 Check peer consistency
516
  Mon Oct 26 05:05:40 2009  - INFO: Checking disk/0 consistency on node node2
517
  Mon Oct 26 05:05:40 2009 STEP 3/6 Allocate new storage
518
  Mon Oct 26 05:05:40 2009  - INFO: Adding new local storage on node1 for disk/0
519
  Mon Oct 26 05:05:41 2009 STEP 4/6 Changing drbd configuration
520
  Mon Oct 26 05:05:41 2009  - INFO: activating a new drbd on node1 for disk/0
521
  Mon Oct 26 05:05:42 2009  - INFO: Shutting down drbd for disk/0 on old node
522
  Mon Oct 26 05:05:42 2009  - WARNING: Failed to shutdown drbd for disk/0 on oldnode: Node is marked offline
523
  Mon Oct 26 05:05:42 2009       Hint: Please cleanup this device manually as soon as possible
524
  Mon Oct 26 05:05:42 2009  - INFO: Detaching primary drbds from the network (=> standalone)
525
  Mon Oct 26 05:05:42 2009  - INFO: Updating instance configuration
526
  Mon Oct 26 05:05:45 2009  - INFO: Attaching primary drbds to new secondary (standalone => connected)
527
  Mon Oct 26 05:05:46 2009 STEP 5/6 Sync devices
528
  Mon Oct 26 05:05:46 2009  - INFO: Waiting for instance instance1 to sync disks.
529
  Mon Oct 26 05:05:46 2009  - INFO: - device disk/0: 13.90% done, 7 estimated seconds remaining
530
  Mon Oct 26 05:05:53 2009  - INFO: Instance instance1's disks are in sync.
531
  Mon Oct 26 05:05:53 2009 STEP 6/6 Removing old storage
532
  Mon Oct 26 05:05:53 2009  - INFO: Remove logical volumes for 0
533
  Mon Oct 26 05:05:53 2009  - WARNING: Can't remove old LV: Node is marked offline
534
  Mon Oct 26 05:05:53 2009       Hint: remove unused LVs manually
535
  Mon Oct 26 05:05:53 2009  - WARNING: Can't remove old LV: Node is marked offline
536
  Mon Oct 26 05:05:53 2009       Hint: remove unused LVs manually
537
  Mon Oct 26 05:05:53 2009 Replacing disk(s) 0 for instance4
538
  Mon Oct 26 05:05:53 2009 STEP 1/6 Check device existence
539
  Mon Oct 26 05:05:53 2009  - INFO: Checking disk/0 on node1
540
  Mon Oct 26 05:05:53 2009  - INFO: Checking volume groups
541
  Mon Oct 26 05:05:53 2009 STEP 2/6 Check peer consistency
542
  Mon Oct 26 05:05:53 2009  - INFO: Checking disk/0 consistency on node node1
543
  Mon Oct 26 05:05:54 2009 STEP 3/6 Allocate new storage
544
  Mon Oct 26 05:05:54 2009  - INFO: Adding new local storage on node2 for disk/0
545
  Mon Oct 26 05:05:54 2009 STEP 4/6 Changing drbd configuration
546
  Mon Oct 26 05:05:54 2009  - INFO: activating a new drbd on node2 for disk/0
547
  Mon Oct 26 05:05:55 2009  - INFO: Shutting down drbd for disk/0 on old node
548
  Mon Oct 26 05:05:55 2009  - WARNING: Failed to shutdown drbd for disk/0 on oldnode: Node is marked offline
549
  Mon Oct 26 05:05:55 2009       Hint: Please cleanup this device manually as soon as possible
550
  Mon Oct 26 05:05:55 2009  - INFO: Detaching primary drbds from the network (=> standalone)
551
  Mon Oct 26 05:05:55 2009  - INFO: Updating instance configuration
552
  Mon Oct 26 05:05:55 2009  - INFO: Attaching primary drbds to new secondary (standalone => connected)
553
  Mon Oct 26 05:05:56 2009 STEP 5/6 Sync devices
554
  Mon Oct 26 05:05:56 2009  - INFO: Waiting for instance instance4 to sync disks.
555
  Mon Oct 26 05:05:56 2009  - INFO: - device disk/0: 12.40% done, 8 estimated seconds remaining
556
  Mon Oct 26 05:06:04 2009  - INFO: Instance instance4's disks are in sync.
557
  Mon Oct 26 05:06:04 2009 STEP 6/6 Removing old storage
558
  Mon Oct 26 05:06:04 2009  - INFO: Remove logical volumes for 0
559
  Mon Oct 26 05:06:04 2009  - WARNING: Can't remove old LV: Node is marked offline
560
  Mon Oct 26 05:06:04 2009       Hint: remove unused LVs manually
561
  Mon Oct 26 05:06:04 2009  - WARNING: Can't remove old LV: Node is marked offline
562
  Mon Oct 26 05:06:04 2009       Hint: remove unused LVs manually
563
  node1#
564

    
565
And now node3 is completely free of instances and can be repaired::
566

    
567
  node1# gnt-node list
568
  Node  DTotal DFree MTotal MNode MFree Pinst Sinst
569
  node1   1.3T  1.3T  32.0G  1.0G 30.2G     3     1
570
  node2   1.3T  1.3T  32.0G  1.0G 30.4G     1     3
571
  node3      ?     ?      ?     ?     ?     0     0
572

    
573
Re-adding a node to the cluster
574
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
575

    
576

    
577
Let's say node3 has been repaired and is now ready to be
578
reused. Re-adding it is simple::
579

    
580
  node1# gnt-node add --readd node3
581
  The authenticity of host 'node3 (172.24.227.1)' can't be established.
582
  RSA key fingerprint is 9f:2e:5a:2e:e0:bd:00:09:e4:5c:32:f2:27:57:7a:f4.
583
  Are you sure you want to continue connecting (yes/no)? yes
584
  Mon Oct 26 05:27:39 2009  - INFO: Readding a node, the offline/drained flags were reset
585
  Mon Oct 26 05:27:39 2009  - INFO: Node will be a master candidate
586

    
587
And is now working again::
588

    
589
  node1# gnt-node list
590
  Node  DTotal DFree MTotal MNode MFree Pinst Sinst
591
  node1   1.3T  1.3T  32.0G  1.0G 30.2G     3     1
592
  node2   1.3T  1.3T  32.0G  1.0G 30.4G     1     3
593
  node3   1.3T  1.3T  32.0G  1.0G 30.4G     0     0
594

    
595
.. note:: If you have the ganeti-htools package installed, you can
596
   shuffle the instances around to have a better use of the nodes.
597

    
598
Disk failures
599
+++++++++++++
600

    
601
A disk failure is simpler than a full node failure. First, a single disk
602
failure should not cause data-loss for any redundant instance; only the
603
performance of some instances might be reduced due to more network
604
traffic.
605

    
606
Let take the cluster status in the above listing, and check what volumes
607
are in use::
608

    
609
  node1# gnt-node volumes -o phys,instance node2
610
  PhysDev   Instance
611
  /dev/sdb1 instance4
612
  /dev/sdb1 instance4
613
  /dev/sdb1 instance1
614
  /dev/sdb1 instance1
615
  /dev/sdb1 instance3
616
  /dev/sdb1 instance3
617
  /dev/sdb1 instance2
618
  /dev/sdb1 instance2
619
  node1#
620

    
621
You can see that all instances on node2 have logical volumes on
622
``/dev/sdb1``. Let's simulate a disk failure on that disk::
623

    
624
  node1# ssh node2
625
  node2# echo offline > /sys/block/sdb/device/state
626
  node2# vgs
627
    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
628
    /dev/sdb1: read failed after 0 of 4096 at 750153695232: Input/output error
629
    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
630
    Couldn't find device with uuid '954bJA-mNL0-7ydj-sdpW-nc2C-ZrCi-zFp91c'.
631
    Couldn't find all physical volumes for volume group xenvg.
632
    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
633
    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
634
    Couldn't find device with uuid '954bJA-mNL0-7ydj-sdpW-nc2C-ZrCi-zFp91c'.
635
    Couldn't find all physical volumes for volume group xenvg.
636
    Volume group xenvg not found
637
  node2#
638

    
639
At this point, the node is broken and if we are to examine
640
instance2 we get (simplified output shown)::
641

    
642
  node1# gnt-instance info instance2
643
  Instance name: instance2
644
  State: configured to be up, actual state is up
645
    Nodes:
646
      - primary: node1
647
      - secondaries: node2
648
    Disks:
649
      - disk/0: drbd8, size 256M
650
        on primary:   /dev/drbd0 (147:0) in sync, status ok
651
        on secondary: /dev/drbd1 (147:1) in sync, status *DEGRADED* *MISSING DISK*
652

    
653
This instance has a secondary only on node2. Let's verify a primary
654
instance of node2::
655

    
656
  node1# gnt-instance info instance1
657
  Instance name: instance1
658
  State: configured to be up, actual state is up
659
    Nodes:
660
      - primary: node2
661
      - secondaries: node1
662
    Disks:
663
      - disk/0: drbd8, size 256M
664
        on primary:   /dev/drbd0 (147:0) in sync, status *DEGRADED* *MISSING DISK*
665
        on secondary: /dev/drbd3 (147:3) in sync, status ok
666
  node1# gnt-instance console instance1
667

    
668
  Debian GNU/Linux 5.0 instance1 tty1
669

    
670
  instance1 login: root
671
  Last login: Tue Oct 27 01:24:09 UTC 2009 on tty1
672
  instance1:~# date > test
673
  instance1:~# sync
674
  instance1:~# cat test
675
  Tue Oct 27 01:25:20 UTC 2009
676
  instance1:~# dmesg|tail
677
  [5439785.235448] NET: Registered protocol family 15
678
  [5439785.235489] 802.1Q VLAN Support v1.8 Ben Greear <greearb@candelatech.com>
679
  [5439785.235495] All bugs added by David S. Miller <davem@redhat.com>
680
  [5439785.235517] XENBUS: Device with no driver: device/console/0
681
  [5439785.236576] kjournald starting.  Commit interval 5 seconds
682
  [5439785.236588] EXT3-fs: mounted filesystem with ordered data mode.
683
  [5439785.236625] VFS: Mounted root (ext3 filesystem) readonly.
684
  [5439785.236663] Freeing unused kernel memory: 172k freed
685
  [5439787.533779] EXT3 FS on sda1, internal journal
686
  [5440655.065431] eth0: no IPv6 routers present
687
  instance1:~#
688

    
689
As you can see, the instance is running fine and doesn't see any disk
690
issues. It is now time to fix node2 and re-establish redundancy for the
691
involved instances.
692

    
693
.. note:: For Ganeti 2.0 we need to fix manually the volume group on
694
   node2 by running ``vgreduce --removemissing xenvg``
695

    
696
::
697

    
698
  node1# gnt-node repair-storage node2 lvm-vg xenvg
699
  Mon Oct 26 18:14:03 2009 Repairing storage unit 'xenvg' on node2 ...
700
  node1# ssh node2 vgs
701
    VG    #PV #LV #SN Attr   VSize   VFree
702
    xenvg   1   8   0 wz--n- 673.84G 673.84G
703
  node1#
704

    
705
This has removed the 'bad' disk from the volume group, which is now left
706
with only one PV. We can now replace the disks for the involved
707
instances::
708

    
709
  node1# for i in instance{1..4}; do gnt-instance replace-disks -a $i; done
710
  Mon Oct 26 18:15:38 2009 Replacing disk(s) 0 for instance1
711
  Mon Oct 26 18:15:38 2009 STEP 1/6 Check device existence
712
  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 on node1
713
  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 on node2
714
  Mon Oct 26 18:15:38 2009  - INFO: Checking volume groups
715
  Mon Oct 26 18:15:38 2009 STEP 2/6 Check peer consistency
716
  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 consistency on node node1
717
  Mon Oct 26 18:15:39 2009 STEP 3/6 Allocate new storage
718
  Mon Oct 26 18:15:39 2009  - INFO: Adding storage on node2 for disk/0
719
  Mon Oct 26 18:15:39 2009 STEP 4/6 Changing drbd configuration
720
  Mon Oct 26 18:15:39 2009  - INFO: Detaching disk/0 drbd from local storage
721
  Mon Oct 26 18:15:40 2009  - INFO: Renaming the old LVs on the target node
722
  Mon Oct 26 18:15:40 2009  - INFO: Renaming the new LVs on the target node
723
  Mon Oct 26 18:15:40 2009  - INFO: Adding new mirror component on node2
724
  Mon Oct 26 18:15:41 2009 STEP 5/6 Sync devices
725
  Mon Oct 26 18:15:41 2009  - INFO: Waiting for instance instance1 to sync disks.
726
  Mon Oct 26 18:15:41 2009  - INFO: - device disk/0: 12.40% done, 9 estimated seconds remaining
727
  Mon Oct 26 18:15:50 2009  - INFO: Instance instance1's disks are in sync.
728
  Mon Oct 26 18:15:50 2009 STEP 6/6 Removing old storage
729
  Mon Oct 26 18:15:50 2009  - INFO: Remove logical volumes for disk/0
730
  Mon Oct 26 18:15:52 2009 Replacing disk(s) 0 for instance2
731
  Mon Oct 26 18:15:52 2009 STEP 1/6 Check device existence
732
733
  Mon Oct 26 18:16:01 2009 STEP 6/6 Removing old storage
734
  Mon Oct 26 18:16:01 2009  - INFO: Remove logical volumes for disk/0
735
  Mon Oct 26 18:16:02 2009 Replacing disk(s) 0 for instance3
736
  Mon Oct 26 18:16:02 2009 STEP 1/6 Check device existence
737
738
  Mon Oct 26 18:16:09 2009 STEP 6/6 Removing old storage
739
  Mon Oct 26 18:16:09 2009  - INFO: Remove logical volumes for disk/0
740
  Mon Oct 26 18:16:10 2009 Replacing disk(s) 0 for instance4
741
  Mon Oct 26 18:16:10 2009 STEP 1/6 Check device existence
742
743
  Mon Oct 26 18:16:18 2009 STEP 6/6 Removing old storage
744
  Mon Oct 26 18:16:18 2009  - INFO: Remove logical volumes for disk/0
745
  node1#
746

    
747
As this point, all instances should be healthy again.
748

    
749
.. note:: Ganeti 2.0 doesn't have the ``-a`` option to replace-disks, so
750
   for it you have to run the loop twice, once over primary instances
751
   with argument ``-p`` and once secondary instances with argument
752
   ``-s``, but otherwise the operations are similar::
753

    
754
     node1# gnt-instance replace-disks -p instance1
755
756
     node1# for i in instance{2..4}; do gnt-instance replace-disks -s $i; done
757

    
758
Common cluster problems
759
-----------------------
760

    
761
There are a number of small issues that might appear on a cluster that
762
can be solved easily as long as the issue is properly identified. For
763
this exercise we will consider the case of node3, which was broken
764
previously and re-added to the cluster without reinstallation. Running
765
cluster verify on the cluster reports::
766

    
767
  node1# gnt-cluster verify
768
  Mon Oct 26 18:30:08 2009 * Verifying global settings
769
  Mon Oct 26 18:30:08 2009 * Gathering data (3 nodes)
770
  Mon Oct 26 18:30:10 2009 * Verifying node status
771
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: unallocated drbd minor 0 is in use
772
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: unallocated drbd minor 1 is in use
773
  Mon Oct 26 18:30:10 2009 * Verifying instance status
774
  Mon Oct 26 18:30:10 2009   - ERROR: instance instance4: instance should not run on node node3
775
  Mon Oct 26 18:30:10 2009 * Verifying orphan volumes
776
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 22459cf8-117d-4bea-a1aa-791667d07800.disk0_data is unknown
777
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data is unknown
778
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta is unknown
779
  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta is unknown
780
  Mon Oct 26 18:30:10 2009 * Verifying remaining instances
781
  Mon Oct 26 18:30:10 2009 * Verifying N+1 Memory redundancy
782
  Mon Oct 26 18:30:10 2009 * Other Notes
783
  Mon Oct 26 18:30:10 2009 * Hooks Results
784
  node1#
785

    
786
Instance status
787
+++++++++++++++
788

    
789
As you can see, *instance4* has a copy running on node3, because we
790
forced the failover when node3 failed. This case is dangerous as the
791
instance will have the same IP and MAC address, wreaking havok on the
792
network environment and anyone who tries to use it.
793

    
794
Ganeti doesn't directly handle this case. It is recommended to logon to
795
node3 and run::
796

    
797
  node3# xm destroy instance4
798

    
799
Unallocated DRBD minors
800
+++++++++++++++++++++++
801

    
802
There are still unallocated DRBD minors on node3. Again, these are not
803
handled by Ganeti directly and need to be cleaned up via DRBD commands::
804

    
805
  node3# drbdsetup /dev/drbd0 down
806
  node3# drbdsetup /dev/drbd1 down
807
  node3#
808

    
809
Orphan volumes
810
++++++++++++++
811

    
812
At this point, the only remaining problem should be the so-called
813
*orphan* volumes. This can happen also in the case of an aborted
814
disk-replace, or similar situation where Ganeti was not able to recover
815
automatically. Here you need to remove them manually via LVM commands::
816

    
817
  node3# lvremove xenvg
818
  Do you really want to remove active logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_data"? [y/n]: y
819
    Logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_data" successfully removed
820
  Do you really want to remove active logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta"? [y/n]: y
821
    Logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta" successfully removed
822
  Do you really want to remove active logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data"? [y/n]: y
823
    Logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data" successfully removed
824
  Do you really want to remove active logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta"? [y/n]: y
825
    Logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta" successfully removed
826
  node3#
827

    
828
At this point cluster verify shouldn't complain anymore::
829

    
830
  node1# gnt-cluster verify
831
  Mon Oct 26 18:37:51 2009 * Verifying global settings
832
  Mon Oct 26 18:37:51 2009 * Gathering data (3 nodes)
833
  Mon Oct 26 18:37:53 2009 * Verifying node status
834
  Mon Oct 26 18:37:53 2009 * Verifying instance status
835
  Mon Oct 26 18:37:53 2009 * Verifying orphan volumes
836
  Mon Oct 26 18:37:53 2009 * Verifying remaining instances
837
  Mon Oct 26 18:37:53 2009 * Verifying N+1 Memory redundancy
838
  Mon Oct 26 18:37:53 2009 * Other Notes
839
  Mon Oct 26 18:37:53 2009 * Hooks Results
840
  node1#
841

    
842
N+1 errors
843
++++++++++
844

    
845
Since redundant instances in Ganeti have a primary/secondary model, it
846
is needed to leave aside on each node enough memory so that if one of
847
its peer node fails, all the secondary instances that have that node as
848
primary can be relocated. More specifically, if instance2 has node1 as
849
primary and node2 as secondary (and node1 and node2 do not have any
850
other instances in this layout), then it means that node2 must have
851
enough free memory so that if node1 fails, we can failover instance2
852
without any other operations (for reducing the downtime window). Let's
853
increase the memory of the current instances to 4G, and add three new
854
instances, two on node2:node3 with 8GB of RAM and one on node1:node2,
855
with 12GB of RAM (numbers chosen so that we run out of memory)::
856

    
857
  node1# gnt-instance modify -B memory=4G instance1
858
  Modified instance instance1
859
   - be/memory -> 4096
860
  Please don't forget that these parameters take effect only at the next start of the instance.
861
  node1# gnt-instance modify …
862

    
863
  node1# gnt-instance add -t drbd -n node2:node3 -s 512m -B memory=8G -o debootstrap instance5
864
865
  node1# gnt-instance add -t drbd -n node2:node3 -s 512m -B memory=8G -o debootstrap instance6
866
867
  node1# gnt-instance add -t drbd -n node1:node2 -s 512m -B memory=8G -o debootstrap instance7
868
  node1# gnt-instance reboot --all
869
  The reboot will operate on 7 instances.
870
  Do you want to continue?
871
  Affected instances:
872
    instance1
873
    instance2
874
    instance3
875
    instance4
876
    instance5
877
    instance6
878
    instance7
879
  y/[n]/?: y
880
  Submitted jobs 677, 678, 679, 680, 681, 682, 683
881
  Waiting for job 677 for instance1...
882
  Waiting for job 678 for instance2...
883
  Waiting for job 679 for instance3...
884
  Waiting for job 680 for instance4...
885
  Waiting for job 681 for instance5...
886
  Waiting for job 682 for instance6...
887
  Waiting for job 683 for instance7...
888
  node1#
889

    
890
We rebooted instances for the memory changes to have effect. Now the
891
cluster looks like::
892

    
893
  node1# gnt-node list
894
  Node  DTotal DFree MTotal MNode MFree Pinst Sinst
895
  node1   1.3T  1.3T  32.0G  1.0G  6.5G     4     1
896
  node2   1.3T  1.3T  32.0G  1.0G 10.5G     3     4
897
  node3   1.3T  1.3T  32.0G  1.0G 30.5G     0     2
898
  node1# gnt-cluster verify
899
  Mon Oct 26 18:59:36 2009 * Verifying global settings
900
  Mon Oct 26 18:59:36 2009 * Gathering data (3 nodes)
901
  Mon Oct 26 18:59:37 2009 * Verifying node status
902
  Mon Oct 26 18:59:37 2009 * Verifying instance status
903
  Mon Oct 26 18:59:37 2009 * Verifying orphan volumes
904
  Mon Oct 26 18:59:37 2009 * Verifying remaining instances
905
  Mon Oct 26 18:59:37 2009 * Verifying N+1 Memory redundancy
906
  Mon Oct 26 18:59:37 2009   - ERROR: node node2: not enough memory on to accommodate failovers should peer node node1 fail
907
  Mon Oct 26 18:59:37 2009 * Other Notes
908
  Mon Oct 26 18:59:37 2009 * Hooks Results
909
  node1#
910

    
911
The cluster verify error above shows that if node1 fails, node2 will not
912
have enough memory to failover all primary instances on node1 to it. To
913
solve this, you have a number of options:
914

    
915
- try to manually move instances around (but this can become complicated
916
  for any non-trivial cluster)
917
- try to reduce memory of some instances to accommodate the available
918
  node memory
919
- if you have the ganeti-htools package installed, you can run the
920
  ``hbal`` tool which will try to compute an automated cluster solution
921
  that complies with the N+1 rule
922

    
923
Network issues
924
++++++++++++++
925

    
926
In case a node has problems with the network (usually the secondary
927
network, as problems with the primary network will render the node
928
unusable for ganeti commands), it will show up in cluster verify as::
929

    
930
  node1# gnt-cluster verify
931
  Mon Oct 26 19:07:19 2009 * Verifying global settings
932
  Mon Oct 26 19:07:19 2009 * Gathering data (3 nodes)
933
  Mon Oct 26 19:07:23 2009 * Verifying node status
934
  Mon Oct 26 19:07:23 2009   - ERROR: node node1: tcp communication with node 'node3': failure using the secondary interface(s)
935
  Mon Oct 26 19:07:23 2009   - ERROR: node node2: tcp communication with node 'node3': failure using the secondary interface(s)
936
  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node1': failure using the secondary interface(s)
937
  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node2': failure using the secondary interface(s)
938
  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node3': failure using the secondary interface(s)
939
  Mon Oct 26 19:07:23 2009 * Verifying instance status
940
  Mon Oct 26 19:07:23 2009 * Verifying orphan volumes
941
  Mon Oct 26 19:07:23 2009 * Verifying remaining instances
942
  Mon Oct 26 19:07:23 2009 * Verifying N+1 Memory redundancy
943
  Mon Oct 26 19:07:23 2009 * Other Notes
944
  Mon Oct 26 19:07:23 2009 * Hooks Results
945
  node1#
946

    
947
This shows that both node1 and node2 have problems contacting node3 over
948
the secondary network, and node3 has problems contacting them. From this
949
output is can be deduced that since node1 and node2 can communicate
950
between themselves, node3 is the one having problems, and you need to
951
investigate its network settings/connection.
952

    
953
Migration problems
954
++++++++++++++++++
955

    
956
Since live migration can sometimes fail and leave the instance in an
957
inconsistent state, Ganeti provides a ``--cleanup`` argument to the
958
migrate command that does:
959

    
960
- check on which node the instance is actually running (has the
961
  command failed before or after the actual migration?)
962
- reconfigure the DRBD disks accordingly
963

    
964
It is always safe to run this command as long as the instance has good
965
data on its primary node (i.e. not showing as degraded). If so, you can
966
simply run::
967

    
968
  node1# gnt-instance migrate --cleanup instance1
969
  Instance instance1 will be recovered from a failed migration. Note
970
  that the migration procedure (including cleanup) is **experimental**
971
  in this version. This might impact the instance if anything goes
972
  wrong. Continue?
973
  y/[n]/?: y
974
  Mon Oct 26 19:13:49 2009 Migrating instance instance1
975
  Mon Oct 26 19:13:49 2009 * checking where the instance actually runs (if this hangs, the hypervisor might be in a bad state)
976
  Mon Oct 26 19:13:49 2009 * instance confirmed to be running on its primary node (node2)
977
  Mon Oct 26 19:13:49 2009 * switching node node1 to secondary mode
978
  Mon Oct 26 19:13:50 2009 * wait until resync is done
979
  Mon Oct 26 19:13:50 2009 * changing into standalone mode
980
  Mon Oct 26 19:13:50 2009 * changing disks into single-master mode
981
  Mon Oct 26 19:13:50 2009 * wait until resync is done
982
  Mon Oct 26 19:13:51 2009 * done
983
  node1#
984

    
985
In use disks at instance shutdown
986
+++++++++++++++++++++++++++++++++
987

    
988
If you see something like the following when trying to shutdown or
989
deactivate disks for an instance::
990

    
991
  node1# gnt-instance shutdown instance1
992
  Mon Oct 26 19:16:23 2009  - WARNING: Could not shutdown block device disk/0 on node node2: drbd0: can't shutdown drbd device: /dev/drbd0: State change failed: (-12) Device is held open by someone\n
993

    
994
It most likely means something is holding open the underlying DRBD
995
device. This can be bad if the instance is not running, as it might mean
996
that there was concurrent access from both the node and the instance to
997
the disks, but not always (e.g. you could only have had the partitions
998
activated via ``kpartx``).
999

    
1000
To troubleshoot this issue you need to follow standard Linux practices,
1001
and pay attention to the hypervisor being used:
1002

    
1003
- check if (in the above example) ``/dev/drbd0`` on node2 is being
1004
  mounted somewhere (``cat /proc/mounts``)
1005
- check if the device is not being used by device mapper itself:
1006
  ``dmsetup ls`` and look for entries of the form ``drbd0pX``, and if so
1007
  remove them with either ``kpartx -d`` or ``dmsetup remove``
1008

    
1009
For Xen, check if it's not using the disks itself::
1010

    
1011
  node1# xenstore-ls /local/domain/0/backend/vbd|grep -e "domain =" -e physical-device
1012
  domain = "instance2"
1013
  physical-device = "93:0"
1014
  domain = "instance3"
1015
  physical-device = "93:1"
1016
  domain = "instance4"
1017
  physical-device = "93:2"
1018
  node1#
1019

    
1020
You can see in the above output that the node exports three disks, to
1021
three instances. The ``physical-device`` key is in major:minor format in
1022
hexadecimal, and 0x93 represents DRBD's major number. Thus we can see
1023
from the above that instance2 has /dev/drbd0, instance3 /dev/drbd1, and
1024
instance4 /dev/drbd2.
1025

    
1026
.. vim: set textwidth=72 :
1027
.. Local Variables:
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.. End: