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@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.


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