[Libvir] storage API and ZFS

Daniel P. Berrange berrange at redhat.com
Thu Oct 18 18:08:28 UTC 2007

On Thu, Oct 18, 2007 at 06:58:38PM +0100, John Levon wrote:
> Accidentally deleted your reply Richard, sorry.
> ZFS 'pools' are aggregates composed of some number of real devices. LVM
> confuses me so I don't know what they map on to, but the basic idea is
> that you can carve filesystems out of such pools at will.

That is the same concept as an LVM volume group.

> You can also carve out 'volumes' - these appear as a disk device in
> /dev/zvol/dsk/poolname/volumename

That is the same concept as an LVM logical volume

> It's the latter that you use in Xen to hold domU root filesystems (or
> you can use a normal file on whatever file system, or a real device, as
> desired).
> What might be tricky is anything that claims to return "space left",
> depending exactly on what you want it to mean. But (I think) certain LVM
> setups have similar issues.

Asking 'space left' for a volume directly isn't really applicable - that's a
property of the file system on the volume instead.  'Space left' in a pool
is basically an indication of how much space is available for allocating
additional pools. Allowing you ask 'is that space to allocate a 10 GB
volume in this pool?' rather than just blindly trying & failing

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