[pve-devel] KVM Live Backup performance

Dietmar Maurer dietmar at proxmox.com
Mon Nov 25 12:26:10 CET 2013

> I have not tested writes yet and doubt I will have time to get to that this week.

To show drawbacks of LVM snapshots, you can use something like:

# dd if=/dev/urandom of=tmp.raw bs=1M

inside the VM during backup.

LVM snapshot will most likely run full, and is very slow:

# time  vmtar ....
ERROR: incomplete read detected
Command exited with non-zero status 255
6.13user 144.59system 21:37.43elapsed 11%CPU (0avgtext+0avgdata 568maxresident)k
129851856inputs+0outputs (0major+180minor)pagefaults 0swaps

Live backup works as expected:

# time vzdump ...
INFO: transferred 68719 MB in 560 seconds (122 MB/s)
INFO: Finished Backup of VM 40000 (00:09:20)
INFO: Backup job finished successfully

real	9m20.527s

Note: it is more than 2 times faster

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