virtualbox I/O 3 times slower than KVM?

[Ted Mittelstaedt]

On 4/30/2011 7:28 PM, typo W wrote:
> Hi, I'm brand new to virtualbox, so pardon me in case I made stupid
> mistakes.  I created a FreeBSD guest out of the regular virtualbox
> port (3.2.12) on FreeBSD 8.2, then timed the copying of a 320MB
> binary file to another file, which took 4 seconds, ie, 80MB/s.  On an
> identical hardware I created a CentOS guest out of KVM running on
> CentOS, and the same operation only takes 1 second.  On both hosts,
> the copy takes 1 second.  That is, virtualbox slowed the copying to
> 1/4 speed on my guest FreeBSD.
>
> Both hosts are Dell R710, with 6 x 600GB 15K SAS drives forming a
> RAID6 with R700 controller with 512MB cache.
>

Try some file copies at the base OS and let us know the results.

I would guess that the FreeBSD hardware RAID device driver for
the R700 controller isn't using the hardware write caching of
the controller.  When the FreeBSD host OS got the file write
call from the virtual box it should have issued the write to the
disk controller and then returned immediately since the write should
have gone into the hardware cache of the controller.

you can also try playing with the sync/async options in the host OS. 
See the mount command for details.  it is kind of pointless to do
sync writes on a caching hardware controller because the entire
point of sync writes is to keep the data from being scrambled
in a crash or if there is sudden power loss - but the cache in the 
hardware array card is more than capable of screwing the filesystem
if that happens.

Ted



> I'm testing in preparation of production servers, so would prefer
> regular ports, ie, 4.0.6 tar ball is out of question for now.
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