Re: 5x slower guest disk performance with virtio disk

["Brian J. Murrell" <brian@interlinx.bc.ca>]

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On 11-12-15 10:47 AM, Stefan Pietsch wrote: 
> 
> Did you try to set the cache of the virtio disk to "none"?

I didn't.  It was set at "default" in virt-manager and I suppose I just
assumed that "default" would be reasonable.

Changing to "none" has had a good effect indeed:

host $ ssh guest dd of=/dev/vdb if=/dev/zero bs=1M oflag=direct count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 49.9241 s, 210 MB/s
host $ ssh guest dd of=/dev/vdb if=/dev/zero bs=1M oflag=direct count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 54.7737 s, 191 MB/s
host $ ssh guest dd of=/dev/vdb if=/dev/zero bs=1M oflag=direct count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 50.9851 s, 206 MB/s
host $ sudo dd of=/dev/datavol/disk1 if=/dev/zero bs=1M oflag=direct count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 31.0545 s, 338 MB/s

So, about 2/3 of host speed now -- which is much better.  Is 2/3 about
normal or should I be looking for more?

Thanks much!

b.


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