[CentOS-virt] Bad Disk Performance of domU

Christopher G. Stach II

cgs at ldsys.net
Wed May 20 16:10:11 UTC 2009

----- "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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