I had the same problem yesterday. I found the solution from this article https://kashyapc.fedorapeople.org/virt/lc-2012/snapshots-handout.html. According to the article it deletes the tracking metadata by libvirt.

You can physically remove the snapshot now that there is no tracking stream data by libvirt

On Wed, Aug 23, 2017 at 4:56 PM, Doug Hughes <doug.hughes@keystonenap.com> wrote:

THat did it! Can you esplain what was going on and how that fixed it? Thanks


On 8/23/2017 10:50 AM, Sakhi Hadebe wrote:
Hi,

Can you try this command:
virsh snapshot-delete serv1r2 snap --metadata




On Wed, Aug 23, 2017 at 4:41 PM, Doug Hughes <doug.hughes@keystonenap.com> wrote:

I'm not sure how this snapshot got created, but, I cannot delete it, and its presence prevents me from creating other snapshots. I don't know if it was created by a command gone amok or something else.

# virsh snapshot-list serv1r2
 Name                 Creation Time             State
------------------------------------------------------------
 snap                 2017-01-30 17:01:11 -0500 shutoff

# virsh snapshot-delete serv1r2 snap --disk-only
error: command 'snapshot-delete' doesn't support option --disk-only

# virsh snapshot-dumpxml serv1r2 snap
<domainsnapshot>
  <name>snap</name>
  <state>shutoff</state>
  <creationTime>1485813671</creationTime>
  <memory snapshot='no'/>
  <disks>
    <disk name='vda' snapshot='external' type='file'>
      <driver type='qcow2'/>
      <source file='/var/lib/libvirt/images/serv1r2-savesnap.qcow2'/>
    </disk>
    <disk name='fda' snapshot='no'/>
    <disk name='hda' snapshot='no'/>
  </disks>

#  ls -l /var/lib/libvirt/images/serv1r2-savesnap.qcow2
ls: cannot access /var/lib/libvirt/images/serv1r2-savesnap.qcow2: No such file or directory

# virsh snapshot-create-as --domain serv1r2 snap --diskspec vda,file=/var/lib/libvirt/flashimages/serv1r2-snap.qcow2  --disk-only --atomic --no-metadata --quiesce
error: internal error: unexpected domain snapshot snap already exists

# virsh snapshot-revert serv1r2 snap
error: unsupported configuration: revert to external snapshot not supported yet

Any idea for breaking out of this box?



--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)

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--
Regards,
Sakhi Hadebe
Engineer: South African National Research Network (SANReN)Competency Area, Meraka, CSIR
 
Tel:   +27 12 841 2308
Fax:   +27 12 841 4223
Cell:  +27 71 331 9622
Email: sakhi@sanren.ac.za

--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)



--
Regards,
Sakhi Hadebe
Engineer: South African National Research Network (SANReN)Competency Area, Meraka, CSIR
 
Tel:   +27 12 841 2308
Fax:   +27 12 841 4223
Cell:  +27 71 331 9622
Email: sakhi@sanren.ac.za