Re: IO on guest is 20 times slower than host

Avi Kivity
2009-03-25T17:54:33Z

Kurt Yoder wrote:
>
> What do you mean about the cache? Is my test fundamentally flawed? I
> *thought* I was testing write speed on the disk...

'dd', without further arguments, will write to the page cache and let
the kernel write the data back at a later time. If you increase the
block size (bs=1M count=1000) you should see much faster times on the
host, I wouldn't be surprised to see 1GB/s.

If you want to test disk speed, use of=/dev/blah oflag=direct. Beware
of destroying your data disk.

Something weird is happening with your system. If you extend the test,
what does 'top' show? On both guest and host.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.