Re: [Xen-users] Re: Xen Disk I/O performance vs native performance: Xen I/O is definitely super super super slow

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Thu, Feb 12, 2009 at 10:02 PM, DOGUET Emmanuel
<Emmanuel.DOGUET@xxxxxxxx> wrote:
> - dd if=/dev/zero of=TEST bs=4k count=1250000 (5Gb for avoid mem cache).

> dom0:  5120000000 bytes (5.1 GB) copied, 139.492 seconds, 36.7 MB/s
> domU    5120000000 bytes (5.1 GB) copied, 279.251 seconds, 18.3 MB/s

Here's what I get using "dd if=/dev/zero of=testfile bs=4k count=524288"

dom0: 2147483648 bytes (2.1 GB) copied, 14.5523 seconds, 148 MB/s
domU: 2147483648 bytes (2.1 GB) copied, 14.8254 seconds, 145 MB/s

Since I only allocate 512M for dom0 and domU, 2G test file is enough
to avoid memory cache effects. As you can see the performance is
similar between dom0 and domU. Maybe you're using HVM? Try "uname -a"
on your domU. If it shows a xen kernel then it's PV.

It might also be because of the difference in disks used or another
I/O-intensive process running on your server, since I got over 140
MB/s while you only get 36 MB/s on dom0.

My point is PV domU should have similar I/O performance to dom0 when
configured correctly (e.g. using LVM or partition-backed storage). If
there's a huge difference (like what you get) then maybe the source of
the problem is elsewhere, not in Xen.

Regards,

Fajar

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