[libvirt-users] Help with understanding and solving snapshot problem

[rolf]

Hello

Fairly new to libvirt.  I’m hoping to both solve a problem with this question as well as learn more detail about how libvirt works.

Using RHEL 6.4 and libvirt version is 0.10.2 and qemu-img version is 0.12.1.2

Using virt-manager I created a VM.  Nothing unusual as far as I can see.  I then added a disk. So I have a second virtio based volume which the guest then mounts as a separate filesystem.  At some stage after that I created a snapshot of the system.  

I can’t delete the snapshot.   The end result is I’d like to create a snapshot that excludes the second (much larger) disk - that is backed up via conventional backup systems.  But the issue is first deleting the snapshot and my understanding of what its saying.

So here is some basic info:

# virsh snapshot-list host1
 Name                 Creation Time             State
------------------------------------------------------------
 snap1-host1           2014-01-19 16:59:10 +1100 shutoff

# 
# virsh snapshot-info host1 --current
Name:           snap1-host1
Domain:         host1
Current:        yes
State:          shutoff
Location:       internal
Parent:         -
Children:       0
Descendants:    0
Metadata:       yes

So I try and delete it:

# virsh snapshot-delete host1 --current

error: Failed to delete snapshot snap1-host1
error: unsupported configuration: deletion of 1 external disk snapshots not supported yet

Why does it say “external” in the above error, when the snapshot-info says its Location is internal? Are they not related ideas?

The img file /var/lib/libvirt/images/host1.img  is not being used by KVM.  the snapshot files are in use instead:

# virsh domblklist host1
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/snap1-host1.qcow2
vdb        /var/lib/libvirt/snap1-host1-db.qcow2
hdc        -

Querying them:

# qemu-img info /var/lib/libvirt/snap1-host1.qcow2 
image: /var/lib/libvirt/snap1-host1.qcow2
file format: qcow2
virtual size: 24G (25769803776 bytes)
disk size: 3.5G
cluster_size: 65536

[root at cocoa libvirt]# qemu-img info /var/lib/libvirt/snap1-host1-db.qcow2 
image: /var/lib/libvirt/snap1-host1-db.qcow2
file format: qcow2
virtual size: 1.6T (1800279089664 bytes)
disk size: 325G
cluster_size: 65536

What have I done wrong and how can I correct this so I can discard the existing snapshot and have a snapshot of the system excluding the second disk (and optionally which I can re-take at intervals and discard old ones)?

Many thanks,

rolf.