[pve-devel] KVM Live Backup performance

Eric Blevins eric at netwalk.com
Thu Nov 21 17:51:57 CET 2013

On the forum there are a number of people who are complaining about high 
load averages on the host and/or in the VM being backed up when using 
the new KVM Live Backup feature.

My suspicion is that having the KVM process move the backup data around 
the performance of the VM is negatively affected. With the KVM process 
using more CPU, performing more IO the VM is starved for resources 
possibly caused by the CPU cache being filled with backup data instead 
of VMs executing code.

I would like to perform some benchmarks where CPU/IO/RAM intensive tasks 
are run inside the VM while performing a LVM Snapshot backup and then a 
KVM Live Backup.  Comparing the completion times of the CPU/IO/RAM tasks 
would allow us to assess what subsystems are affected, good or bad, by 
KVM Live Backup.

Since all of the LVM Snapshot code was removed I am unable to perform 
the above benchmarks, anyone have a suggestion how we could perform such 
tests easily?


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