[pve-devel] savevm tests

Dietmar Maurer dietmar at proxmox.com
Fri Aug 31 10:09:10 CEST 2012

> >>Why not possible? We can simply allocate a normal volume, and store
> state there?
> I want to say, without hacking qemu code ;) But maybe it's possible, but is
> really difficult.

looks easy to me ;-) I am just exploring the savevm.c code - will send more
details later.

> It need to code a nexenta block driver for qemu (forking libiscsi), and a
> volume management to do space,save the vmstate,...
> Seem really difficult to do, and maintain in time

No, I guess there will be a simpler solutions. 

> >>We have VM which use qcow2, sheepdog, rdb and nexenta at the same
> time. How should that work?
> yes indeed,
> But I really don't think that users will mix all the storage on same vm. (and
> have enough money to build and maintain all the storage clusters ;) But, if
> they really want to do it,

They will mix, I am 100% sure about that ;-)

> I see 2 kinds of storages for snapshots:
> - qemu "internal" storage, using qemu block drivers.
>     - qcow2
>     - rbd
>     - sheepdog
> - external storage
>  like -nexenta,
>       and maybe other futur storage like:
>       -lvm (dm-thinp, for local snapshot by exemple)
>       - why not btrfs in the future
>       -netapp storage(I say that because I'm planning to build a big big netapp
> cluster for a customer in the coming months)
>       -...
> qemu internal storage, must have same features (missing rbd vmstate, but it
> should come soon).
> They also have the same snapshots/rollback capabilities. (multi branch tree,
> read/write snapshots) So we can mix them on the same vm, and use
> snapshots.
> But we can't mix them with other storages. (savevm exit if it detect a storage
> without savevm capability, like raw file,blockdevice,iscsi device)
> external storage:
> they maybe have not the same snapshots capabilities, no vmstate.
> So theses storage could not be mixed with other storages, if we want to use
> snapshot.
> We just need to check the differents mixed storage used by the vm before
> allow the snapshots.
> What do you think ?

I think we can simply call an external helper for such storage types. Will dig deeper
into qemu code now.

- Dietmar

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