Re: IO on guest is 20 times slower than host

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Kurt Yoder wrote:

I see. I looked up another test: using hdparm -t. It doesn't show the situation as quite so bad, but the guest is still a little over half the speed of the host:

me@host:~$ sudo hdparm -t /dev/mapper/HW_RAID-ROOT

/dev/mapper/HW_RAID-ROOT:
 Timing buffered disk reads:  282 MB in  3.00 seconds =  93.92 MB/sec

me@guest:~# hdparm -t /dev/vda

/dev/vda:
 Timing buffered disk reads:  156 MB in  3.03 seconds =  51.56 MB/sec

This is reasonable. IDE emulation is not expected to be as fast as the host.

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

If I extend the test thusly on the guest:

dd if=/dev/zero of=/bigfile count=10000000

I see 100% CPU utilization on the guest, and 100% CPU utilization on one of the host cores.

Can you post 'vmstat 1' snippets on both guest and host while this is running?

Oh, and try switching to the deadline I/O scheduler on the host instead of the default cfq.


--
error compiling committee.c: too many arguments to function

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