[virt-tools-list] virt-manager and iSCSI

Eric Blake eblake at redhat.com
Thu Apr 5 17:30:13 UTC 2012

On 04/05/2012 11:13 AM, Alan McKay wrote:
> OK, I'm just poking around virsh and what commands are there, and I have a
> feeling I've found the issue.
> I took my iSCSI disk and made an XML file for a "pool" but I have a feeling
> I should have made an XML file for a "volume"
> Could that be the case?
> So it sees something out there it is just confused about exactly what it is.
> So I just need to remove that pool and then make a file for a volume and
> add it?

A pool is like a directory (in fact, you can make a pool that wraps a
directory, if you are using files on a file system instead of LUNs in an
iSCSI setup).  A storage volume is the space that can hold a single disk
image (in a directory-based storage pool, each storage volume is a file;
in an iSCSI setup, each LUN is a a storage volume).

You can't have a storage volume without also having a storage pool to
hold the volume.  So you need XML for both.

[By the way, libvirt will let you use absolute pathnames as disk images
even if they aren't available as a storage volume.  But someday I'd like
to improve that, by creating a notion of transient storage pools that
are auto-created by any <domain> that references a file that is not
already part of an existing storage pool, as well as improving the
<domain> XML to let you specify pool:volume notation rather than
absolute paths to files as a way to more effectively tie together the
operations you can do on a storage volume not in use by any domain, and
the hot-modification operations you can do via a running domain.  In
particular, making domain and storage pool play nicer together will make
it easier to write abstractions such as snapshots on top of LVM volumes,
rather than the current limitation of qemu snapshots requiring qcow2
disk files.  But that's all plans for future code, and may take several

Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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