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[Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2
[Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm)
Fri, 25 Mar 2011 14:33:30 -0000
The current upstream qemu.git from git://git.savannah.nongnu.org/qemu.git
also has the slow savevm. However, it's loadvm takes only a few seconds.
** Also affects: qemu
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virsh snapshot-create too slow (kvm, qcow2, savevm)
Status in QEMU:
Status in “qemu-kvm” package in Ubuntu:
# time virsh snapshot-create 1
* Taking snapshot of a running KVM virtual machine
Domain snapshot 1300983161 created
* Snapshot taken after few seconds instead of minutes.
* Ubuntu Natty Narwhal upgraded from Lucid and Meerkat, fully updated.
* Stock natty packages of libvirt and qemu installed (libvirt-bin
0.8.8-1ubuntu5; libvirt0 0.8.8-1ubuntu5; qemu-common 0.14.0+noroms-
0ubuntu3; qemu-kvm 0.14.0+noroms-0ubuntu3).
* Virtual machine disk format is qcow2 (debian 5 installed)
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 1.2G
ID TAG VM SIZE DATE VM CLOCK
1 snap01 48M 2011-03-24 09:46:33 00:00:58.899
2 1300979368 58M 2011-03-24 11:09:28 00:01:03.589
3 1300983161 57M 2011-03-24 12:12:41 00:00:51.905
* qcow2 disk is stored on ext4 filesystem, without RAID or LVM or any
* running guest VM takes about 40M RAM from inside, from outside 576M
are given to that machine
* host has fast dual-core pentium cpu with virtualization support,
around 8G of RAM and 7200rpm harddrive (dd from urandom to file gives
* running processes: sshd, atd (empty), crond (empty), libvirtd, tmux,
bash, rsyslogd, upstart-socket-bridge, udevd, dnsmasq, iotop (python)
* networking is done by bridging and bonding
* Under root, command 'virsh create-snapshot 1' is issued on booted
and running KVM machine with debian inside.
* After about four minutes, the process is done.
* 'iotop' shows two 'kvm' processes reading/writing to disk. First one
has IO around 1500 K/s, second one has around 400 K/s. That takes
about three minutes. Then first process grabs about 3 M/s of IO and
suddenly dissapears (1-2 sec). Then second process does about 7.5 M/s
of IO for around a 1-2 minutes.
* Snapshot is successfuly created and is usable for reverting or
* Pretty much the same behaviour occurs when command 'savevm' is
issued directly from qemu monitor, without using libvirt at all
(actually, virsh snapshot-create just calls 'savevm' to the monitor
* This behaviour was observed on lucid, meerkat, natty and even with
git version of libvirt (f44bfb7fb978c9313ce050a1c4149bf04aa0a670).
Also slowsave packages from
Thank you for helping to solve this issue!
DistroRelease: Ubuntu 11.04
Package: libvirt-bin 0.8.8-1ubuntu5
ProcVersionSignature: Ubuntu 2.6.38-7.38-server 2.6.38
Uname: Linux 2.6.38-7-server x86_64
Date: Thu Mar 24 12:19:41 2011
InstallationMedia: Ubuntu-Server 10.04.2 LTS "Lucid Lynx" - Release amd64
UpgradeStatus: No upgrade log present (probably fresh install)
- [Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm),
Serge Hallyn <=
- [Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm), Michael Tokarev, 2011/03/25
- [Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm), Serge Hallyn, 2011/03/25
- [Qemu-devel] [Bug 741887] Re: virsh snapshot-create too slow (kvm, qcow2, savevm), mkopta, 2011/03/25