CentOS virt - Oct 2012 - unknown command: 'snapshot_blkdev'

I am trying to make a snapshot with this command:

virsh snapshot-create vm01 --disk-only --atomic


the error is:
error: operation failed: Failed to take snapshot: unknown command:
'snapshot_blkdev


the error come from the --disk-only argument

Did tried to google on the subject but no solid information on the matter.

Thanks in advance


Regards

Rudi
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