Synnefo » snf-ganeti » ganeti-local

Disk/Net parameters

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Current State and shortcomings

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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

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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.