Re: [libvirt] libvirtd and LVM snapshots
Daniel P. Berrange:
http://libvirt.org/formatstorage.html#StorageVolBacking
This is currently support for Cow, QCow, QCow2, VMDK and LVM storage
types. Some of these allow for the underling backing store to be
writable, others require that its readonly.
I tried the following under libvirt 0.6.0:
vol = pool.createXML("""<volume type="block">
<name>hurgle</name> <capacity>2147483648</capacity>
<backingStore> <path>/dev/VMs/test-disk</path>
<format>raw</format> </backingStore> </volume>""",
0)
It promptly created a volume, but not as a copy-on-write snapshot:
"dmsetup ls --target snapshot" shows nothing, and the image has none of
the data from the test-disk volume.
The pool I used to create these volumes is clearly LVM:
virsh # pool-dumpxml VMs
<pool type='logical'>
<name>VMs</name>
<uuid>bde8f8ed-7e65-8323-ea93-51223d86fedd</uuid>
<capacity>66433581056</capacity>
<allocation>2281701376</allocation>
<available>64151879680</available>
<source>
<name>VMs</name>
<format type='lvm2'/>
</source>
<target>
<path>/dev/VMs</path>
<permissions>
<mode>0700</mode>
<owner>0</owner>
<group>0</group>
</permissions>
</target>
</pool>
You mentioned some constraints about permissions earlier, but I would
have expected that to raise an exception--vol is a valid volume object
and I can query it and mkfs it and so forth. The test-disk volume is
completely quiescent and unmounted. Do I need to prepare it in some
other way to make it suitable for livirt to use as the base of a
snapshot?
(Just for sanity's sake, I verified that libvirt.getVersion() returns
6000)
--
"Forget the damned motor car Nick Moffitt
and build cities for lovers and friends." nick(a)zork.net
-- Lewis Mumford