From: Helga Velroyen Date: Thu, 21 Feb 2013 10:21:46 +0000 (+0100) Subject: Update design doc about free space reporting X-Git-Tag: v2.8.0beta1~311 X-Git-Url: https://code.grnet.gr/git/ganeti-local/commitdiff_plain/74df4a9933c63105736ad6517764bb872c9daa32 Update design doc about free space reporting This patch updates the design doc "Design correct reporting of storage free space". The modifications were chosen to not conflict with any future changes of Ganeti regarding storage pools. Signed-off-by: Helga Velroyen Reviewed-by: Guido Trotter --- diff --git a/doc/design-storagespace.rst b/doc/design-storagespace.rst index 919479f..46e07ec 100644 --- a/doc/design-storagespace.rst +++ b/doc/design-storagespace.rst @@ -20,21 +20,19 @@ interaction with different storage types. Configuration changes --------------------- -Each storage type will have a new "pools" parameter added (type list of -strings). This will be list of vgs for plain and drbd (note that we make -no distinction at this level between allowed vgs and metavgs), the list -of rados pools for rados, or the storage directory for file and -sharedfile. The parameters already present in the cluster config object -will be moved to the storage parameters. - -Since currently file and sharedfile only support a single directory this -list will be limited to one. In the future if we'll have support for -more directories, or for per-nodegroup directories this can be changed. - -Note that these are just "mechanisms" parameters that define which -storage pools the cluster can use. Further filtering about what's -allowed can go in the ipolicy, but these changes are not covered in this -design doc. +Add a new attribute "enabled_storage_methods" (type: list of strings) to the +cluster config which holds the types of storages, for example, "plain", "drbd", +or "ext". We consider the first one of the list as the default method. + +For file storage, we'll report the storage space on the file storage dir, +which is currently limited to one directory. In the future, if we'll have +support for more directories, or for per-nodegroup directories this can be +changed. + +Note that the abovementioned enabled_storage_methods are just "mechanisms" +parameters that define which storage methods the cluster can use. Further +filtering about what's allowed can go in the ipolicy, but these changes are +not covered in this design doc. Since the ipolicy currently has a list of enabled storage types, we'll use that to decide which storage type is the default, and to self-select @@ -47,17 +45,23 @@ RPC changes ----------- The noded RPC call that reports node storage space will be changed to -accept a list of , string tuples. For each of them it will -report the free amount of space found on storage as known by the -requested method. Methods are for example ``lvm``, ``filesystem``, -``rados``, and the key would be a volume group name in the case of lvm, -a directory name for the filesystem and a rados pool name, for -rados_pool. +accept a list of , string tuples. For each of them, it will +report the free amount of storage space found on storage as known +by the requested storage type method. For example methods are ``lvm``, +``filesystem``, or ``rados``, and the key would be a volume group name, in +the case of lvm, a directory name for the filesystem and a rados pool name +for rados storage. + +For now, we will implement only the storage reporting for non-shared storage, +that is ``filesystem`` and ``lvm``. For shared storage methods like ``rados`` +and ``ext`` we will not implement a free space calculation, because it does +not make sense to query each node for the free space of a commonly used +storage. Masterd will know (through a constant map) which storage type uses which method for storage calculation (i.e. ``plain`` and ``drbd`` use ``lvm``, -``file`` and ``sharedfile`` use ``filesystem``, etc) and query the one -needed (or all of the needed ones). +``file`` uses ``filesystem``, etc) and query the one needed (or all of the +needed ones). Note that for file and sharedfile the node knows which directories are allowed and won't allow any other directory to be queried for security @@ -71,20 +75,49 @@ These calculations will be implemented in the node storage system Ganeti reporting ---------------- -``gnt-node list`` will by default report information just about the -default storage type. It will be possible to add fields to ask about -other ones, if they're enabled. - -``gnt-node info`` will report information about all enabled storage -types, without querying them (just say which ones are supported -according to the cluster configuration). - -``gnt-node list-storage`` will change to report information about all -available storage pools in each storage type. An extra flag will be -added to filter by storage pool name (alternatively we can implement -this by allowing to query by a list of ``type:pool`` string tuples to -have a more comprehensive filter). - +`gnt-node list`` can be queried for the different storage methods, if they +are enabled. By default, it will just report information about the default +storage method. Examples:: + + > gnt-node list + Node DTotal DFree MTotal MNode MFree Pinst Sinst + mynode1 3.6T 3.6T 64.0G 1023M 62.2G 1 0 + mynode2 3.6T 3.6T 64.0G 1023M 62.0G 2 1 + mynode3 3.6T 3.6T 64.0G 1023M 62.3G 0 2 + + > gnt-node list -o dtotal/lvm,dfree/rados + Node DTotal (Lvm, myvg) DFree (Rados, myrados) + mynode1 3.6T - + mynode2 3.6T - + +Note that for drbd, we only report the space of the vg and only if it was not +renamed to something different than the default volume group name. With this +design, there is also no possibility to ask about the meta volume group. We +restrict the design here to make the transition to storage pools easier (as it +is an interim state only). It is the administrator's responsibility to ensure +that there is enough space for the meta volume group. + +When storage pools are implemented, we switch from referencing the storage +method to referencing the storage pool name. For that, of course, the pool +names need to be unique over all storage methods. For drbd, we will use the +default 'lvm' storage pool and possibly a second lvm-based storage pool for +the metavg. It will be possible to rename storage pools (thus also the default +lvm storage pool). There will be new functionality to ask about what storage +pools are available and of what type. + +``gnt-cluster info`` will report which storage methods are enabled, i.e. +which ones are supported according to the cluster configuration. Example +output:: + + > gnt-cluster info + [...] + Cluster parameters: + - [...] + - enabled storage methods: plain (default), drbd, lvm, rados + - [...] + +``gnt-node list-storage`` will not be affected by any changes, since this design +describes only free storage reporting for non-shared storage methods. Allocator changes ----------------- @@ -96,6 +129,10 @@ made. Note that for DRBD nowadays we ignore the case when vg and metavg are different, and we only consider the main VG. Fixing this is outside the scope of this design. +With this design, we ensure forward-compatibility with respect to storage +pools. For now, we'll report space for all available (non-shared) storage +types, in the future, for all available storage pools. + Rebalancing changes ------------------- @@ -109,6 +146,24 @@ Hspace will by default report by assuming the allocation will happen on the default storage for the cluster/nodegroup. An option will be added to manually specify a different storage. +Interactions with Partitioned Ganeti +------------------------------------ + +Also the design for :doc:`Partitioned Ganeti ` deals +with reporting free space. Partitioned Ganeti has a different way to +report free space for LVM on nodes where the ``exclusive_storage`` flag +is set. That doesn't interact directly with this design, as the specific +of how the free space is computed is not in the scope of this design. +But the ``node info`` call contains the value of the +``exclusive_storage`` flag, which is currently only meaningful for the +LVM back-end. Additional flags like the ``external_storage`` flag +for lvm might be useful for other storage types as well. We therefore +extend the RPC call with , to ,, to +include any storage-method specific parameters in the RPC call. + +The reporting of free spindles, also part of Partitioned Ganeti, is not +concerned with this design doc, as those are seen as a separate resource. + .. vim: set textwidth=72 : .. Local Variables: .. mode: rst