[Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm)

[Michael Tokarev]

savevm _is_ slow, because it's writing to a qcow2 file with full
(meta)data allocation which is terrible slow since 0.13 (and 0.12.5)
unless you use cache=unsafe.  It's the same slowdown as observed with
default cache mode when performing an operating system install into a
freshly created qcow2 - it may take several hours.  To verify, run
`iostat -dkx 5' and see how busy (the last column) your disk is during
the save - I suspect it'll be about 100%.

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https://bugs.launchpad.net/bugs/741887

Title:
  virsh snapshot-create too slow (kvm, qcow2, savevm)