X-Git-Url: https://code.grnet.gr/git/ganeti-local/blobdiff_plain/5b18ff3bd72b182e6330fc8e1c6386cee484a6d4..ba55d062da8dfb89a37afc2f13f2e689d0094829:/doc/design-2.1.rst

diff --git a/doc/design-2.1.rst b/doc/design-2.1.rst
index 70c9557..25f75fe 100644
--- a/doc/design-2.1.rst
+++ b/doc/design-2.1.rst
@@ -110,6 +110,83 @@ compatibility with 2.0.
 The code to export the list of VNC password files from the hypervisors to
 RedistributeConfig will be shared between the KVM and xen-hvm hypervisors.
 
+Disk/Net parameters
+~~~~~~~~~~~~~~~~~~~
+
+Current State and shortcomings
+++++++++++++++++++++++++++++++
+
+Currently disks and network interfaces have a few tweakable options and all the
+rest is left to a default we chose. We're finding that we need more and more to
+tweak some of these parameters, for example to disable barriers for DRBD
+devices, or allow striping for the LVM volumes.
+
+Moreover for many of these parameters it will be nice to have cluster-wide
+defaults, and then be able to change them per disk/interface.
+
+Proposed changes
+++++++++++++++++
+
+We will add new cluster level diskparams and netparams, which will contain all
+the tweakable parameters. All values which have a sensible cluster-wide default
+will go into this new structure while parameters which have unique values will not.
+
+Example of network parameters:
+  - mode: bridge/route
+  - link: for mode "bridge" the bridge to connect to, for mode route it can
+    contain the routing table, or the destination interface
+
+Example of disk parameters:
+  - stripe: lvm stripes
+  - stripe_size: lvm stripe size
+  - meta_flushes: drbd, enable/disable metadata "barriers"
+  - data_flushes: drbd, enable/disable data "barriers"
+
+Some parameters are bound to be disk-type specific (drbd, vs lvm, vs files) or
+hypervisor specific (nic models for example), but for now they will all live in
+the same structure. Each component is supposed to validate only the parameters
+it knows about, and ganeti itself will make sure that no "globally unknown"
+parameters are added, and that no parameters have overridden meanings for
+different components.
+
+The parameters will be kept, as for the BEPARAMS into a "default" category,
+which will allow us to expand on by creating instance "classes" in the future.
+Instance classes is not a feature we plan implementing in 2.1, though.
+
+Non bridged instances support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Current State and shortcomings
+++++++++++++++++++++++++++++++
+
+Currently each instance NIC must be connected to a bridge, and if the bridge is
+not specified the default cluster one is used. This makes it impossible to use
+the vif-route xen network scripts, or other alternative mechanisms that don't
+need a bridge to work.
+
+Proposed changes
+++++++++++++++++
+
+The new "mode" network parameter will distinguish between bridged interfaces
+and routed ones.
+
+When mode is "bridge" the "link" parameter will contain the bridge the instance
+should be connected to, effectively making things as today. The value has been
+migrated from a nic field to a parameter to allow for an easier manipulation of
+the cluster default.
+
+When mode is "route" the ip field of the interface will become mandatory, to
+allow for a route to be set. In the future we may want also to accept multiple
+IPs or IP/mask values for this purpose. We will evaluate possible meanings of
+the link parameter to signify a routing table to be used, which would allow for
+insulation between instance groups (as today happens for different bridges).
+
+For now we won't add a parameter to specify which network script gets called
+for which instance, so in a mixed cluster the network script must be able to
+handle both cases. The default kvm vif script will be changed to do so. (Xen
+doesn't have a ganeti provided script, so nothing will be done for that
+hypervisor)
+
 External interface changes
 --------------------------