Mailinglist Archive: opensuse (1468 mails)

[Sandy Drobic <opensuse@xxxxxxxxx>]

Lars Marowsky-Bree wrote:
> On 2009-06-02T22:07:17, Zhang Weiwu <zhangweiwu@xxxxxxxxxx> wrote:
>
> > As far as I know if the hard disk of the guest os is an image file on
> > the host OS, the host OS treats it as a file and offer to cache it in
> > the main memory. However if vmplayer access a partition or harddisk it
> > is not cached by the host OS's file system. That might make it even
> > slower. Unless of course the database is in particular on a raw device
> > that is directly accessed from the guest OS, as Sandy pointed out.
>
> The caching doesn't make a difference, as it is not really different.

The question itself is not relevant. Fact is that performance will increase a
lot if you use a raw device.

How ineffective VMWare disk access within a VM is I can see even on my small
server at home. The server has a raid5 with 5 disks on a 3ware controller.
Even if I only use a VM as a normal user workstation (for email/browers etc
with few write access) the iowait increases a lot. Before I installed vmware i
practically never had iowait on my server, now I see iowait all the time in my
munin graphs.

Even at our company on our ESX Cluster with the VMFS on a SAN I have problems
with some VMs due to lacking i/o performance. :-((

If you want to be happy with VMs you will have to optimize I/O as good as
possible. :-/

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