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

["DOGUET Emmanuel" <Emmanuel.DOGUET@xxxxxxxx>]

I do '5G 'test because linux FS have very good caching system.. and the RAID 
controler too. 

For my domU, I'm agree with you but I don't find the problem. And what about 
the qemu-dm.. it seem to be a HVM functionnality?


dom0:
Linux host33 2.6.18-128.el5xen #1 SMP Wed Dec 17 12:01:40 EST 2008 x86_64 
x86_64 x86_64 GNU/Linux

domU
Linux host33-v1 2.6.18-128.el5xen #1 SMP Wed Dec 17 12:01:40 EST 2008 x86_64 
x86_64 x86_64 GNU/Linux


Bye


>-----Message d'origine-----
>De : Fajar A. Nugraha [mailto:fajar@xxxxxxxxx] 
>Envoyé : vendredi 13 février 2009 05:11
>À : DOGUET Emmanuel
>Cc : xen-users@xxxxxxxxxxxxxxxxxxx
>Objet : Re: [Xen-users] Re: Xen Disk I/O performance vs native 
>performance: Xen I/O is definitely super super super slow
>
>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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