I am unable to reproduce that - for me LVM and Live backup are about the same
speed.
Can you see the effect if you dump backup output directly to /dev/null?
# /usr/lib/qemu-server/vmtar '/etc/pve/qemu-server/108.conf' 'qemu-server.conf'
'/dev/vmdisks/test-snapshot' 'vm-disk'>/dev/null
# vzdump <VMID> -stdout>/dev/null
There is little difference reading inside the VM when writing to
/dev/null, 117MB/sec vs 131MB/sec with LVM.
Here is the best way I have to demonstrate the problem, simulate slow
backup media using cstream.
Slower backup media results in greater IO performance loss in the VM.
vzdump <vmid> -stdout|cstream -t 60000000 > /dev/null
In the VM I ran:
dd if=/dev/vdb of=/dev/null bs=1M count=8192 skip=2400
140MB/sec Limit, 109 MB/s Read speed in VM
120MB/sec Limit, 95.6 MB/s Read speed in VM
100MB/sec Limit, 80.3 MB/s Read speed in VM
80MB/sec Limit, 65.6 MB/s Read speed in VM
60MB/sec Limit, 47.2 MB/s Read speed in VM
40MB/sec Limit, 31.8 MB/s Read speed in VM
With LVM snapshot backups the VM does not suffer performance problems if
the backup media is slow, the backup simply takes longer.
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