[libvirt] [PATCH] ZFS: Support sparse volumes

Richard Laager rlaager at wiktel.com
Tue Mar 15 05:46:57 UTC 2016


On 03/05/2016 08:35 AM, Roman Bogorodskiy wrote:
> What if allocation specified will be much larger than capacity?
>
> Neither zfs nor virStorageBackendZFSCreateVol() prevent from creating a
> volume with:
>
>    --capacity 2G --allocation 4G

Is this necessary to support? I don't see a use case where this is 
helpful. If not, the easy solution seems to be to prohibit it.

If you really want to support this, then I suppose we can just remove 
the clamping, which leads to...

> What's the reason to limit displayed allocation?

I didn't want --capacity 1G --allocation 1G to show as 1.03G allocation.

> PS I noticed that it could be an issue to set refreservation larger than
> volsize with ZFS on Linux:
>      https://github.com/zfsonlinux/zfs/issues/2468.
>
> The issue is still open and at this moment I cannot check if I can
> reproduce that on Linux.

I can reproduce this. Setting the refreservation as part of the initial 
`zfs create` works, but it is not possible to do with `zfs set` later.

-- 
Richard




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