[CentOS-virt] Bad Disk Performance of domU

[Mathew S. McCarrell]

In general, disk performance on a domU will always be lower than on a dom0.
That being said, I agree with Christopher that is sounds like you are using
a sparse disk file.

Did you create this VM with virt-install?  If so, you can pass the
--nonsparse option to virt-install when creating the VM to allocate all the
disk space when creating the VM.

Matt

--
Mathew S. McCarrell
Clarkson University '10

mccarrms at gmail.com
mccarrms at clarkson.edu


On Wed, May 20, 2009 at 12:35 PM, Francisco Pérez <fperez.x at gmail.com>wrote:

> LVM on dom0 or domu?
>
> 2009/5/20 Christopher G. Stach II <cgs at ldsys.net>
>
> ----- "Francisco Pérez" <fperez.x at gmail.com> wrote:
>>
>> > I guess the bad performance it goes with the writing. For example on
>> > decompression of a big tar.gz, installing rpm packages. Also on
>> > restoring a MySQL Database...
>> >
>> > The first clue when i knew that something were wrong was on the FS
>> > formating stage. It took really long time to format 40 GB to ext3. I
>> > did the same on other machine with a sata disk... surprise! same
>> > software and hardware config except for the inferior disk type and did
>> > it in no time.
>>
>> It sounds like your the virtual disk file is sparse.  If that's the case,
>> you traded performance for space.  It not only has to deal with the
>> underlying filesystem, but it allocates the space on demand and hits that
>> filesystem's journal.  Try an LVM logical disk and see how that performs.
>>
>> --
>> Christopher G. Stach II
>>
>>
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>
>
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