[libvirt-users] io=native

Troels Arvin troels at arvin.dk
Thu Jun 2 15:27:37 UTC 2011


Regarding KVM - in particular RHEL 6.1 x86_64:

I just did a set of benchmarks comparing the effect of

<driver name='qemu' type='raw' cache='none' io='native'/>
<driver name='qemu' type='raw' cache='none'/>

Using Oracle's "orion" tool with an XIV backend, I got:

With io='native':
Maximum Large MBPS=964.41
Maximum Small IOPS=11797
Minimum Small Latency=7.57

WithOUT io='native':
Maximum Large MBPS=727.42
Maximum Small IOPS=7793
Minimum Small Latency=7.56

In other words, setting the io-attribute to 'native' yields a significant 
performance improvement.

I wonder why KVM doesn't simply default to using io='native'. If that 
can't happen, then I wonder why libvirt doesn't set io='native' for 
storage attached to a guest after creation. (virt-manager sets io='native' 
for the first storage, attached during guest setup, but seems to forget 
for subsequent block-device additions).

Troels Arvin <troels at arvin.dk>

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