Re: 5x slower guest disk performance with virtio disk

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* Brian J. Murrell <brian@xxxxxxxxxxxxxxx> [2011-12-15 15:28]:
> I have a CentOS 6 host system running a CentOS 6 KVM guest and the
> guest seems to get about 5x slower disk throughput than the host:
> 
> host $ sudo dd of=/dev/datavol/disk1 if=/dev/zero bs=1M oflag=direct count=50000
> 50000+0 records in
> 50000+0 records out
> 52428800000 bytes (52 GB) copied, 150.36 s, 349 MB/s
> host $ ssh guest dd of=/dev/vdb if=/dev/zero bs=1M oflag=direct count=50000
> 50000+0 records in
> 50000+0 records out
> 52428800000 bytes (52 GB) copied, 731.007 s, 71.7 MB/s
> 
> This is actually a vast improvement over earlier tests where it was a
> factor of 40x difference.  But even still, I thought virtio disks were
> supposed to be much closer to native host speed than 5x.

--- snip ---


Did you try to set the cache of the virtio disk to "none"?


Regards,
Stefan
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