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

[mkopta]

I confirm that without 'cache' option, I have got from iostat those
result while doing 'savevm'

Device: sda
rrqm/s: 0.00
wrqm/s: 316.00
r/s: 0.00
w/s: 94.80
rkB/s: 0.00
wkB/s: 1541.60
avgrq-sz: 32.52
avgqu-sz: 0.98
await: 10.32
svctm: 10.10
%util: 95.76

I also confirm, that when option 'cache=unsafe' is used, snapshot (from
qemu monitor) is done as quickly as it should (few seconds).

I am not sure if this is a solution or workaround or just a closer
description of a bug.

http://libvirt.org/formatdomain.html#elementsDisks describes option
'cache'. When I use that (cache="none") it spits out:

error: Failed to create domain from vm.xml
error: internal error process exited while connecting to monitor: kvm: -drive file=/home/dum8d0g/vms/deb.qcow2,if=none,id=drive-ide0-0-0,boot=on,format=qcow2,cache=none: could not open disk image /home/dum8d0g/vms/deb.qcow2: Invalid argument

When that option is removed, domain is created successfuly. I guess I
have another bugreport to fill.

So, for me, the issue is somehow solved from the qemu side. I think,
this could be marked as wontfix.

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

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