Re: [Xen-users] Raid1 performance

[blub@xxxxxxxx]

> On Thu, Apr 08, 2010 at 08:23:19PM +0200, blub@xxxxxxxx wrote:
>> > On Thu, Apr 08, 2010 at 07:00:11PM +0200, blub@xxxxxxxx wrote:
>> >> hello
>> >> i've been trying to achieve reasonable disk i/o performance on xen.
>> >> on debian 5.0.4 (xen 3.2.1, kernel 2.6.26) the pv/hvm performance is
>> >> alright with a raid1 inside the domU. unfortunately the qemu version
>> >> (0.9.0) does not cover my needs.
>> >>
>> >> so i've been trying xen 3.4.2 & 4.0.0rc8 on gentoo (2.6.31)
>> >> on both versions, the disk i/o performance drops to zero when copying
>> >> large files. initially the performance is ok (~30mbyte/s) but drops
>> to
>> >> zero after ~300mb, i've tried it with wget/ftp/scp
>> >> this happens with both PV & HVM domU's. i've tried multiple nic
>> drivers
>> >>
>> >> the performance seems alright if no raid1 is running on the domU
>> >> i cannot run the domU raid1's on the dom0 since there are multiple
>> dom0s
>> >> connecting to multiple FC SAN's and the raid1's are done across the
>> >> SAN's
>> >>
>> >> (btw, the performance with raid1's on the SAN's is excellent on dom0)
>> >>
>> >> anyone else has experienced this issue?
>> >>
>> >
>> > Did you make sure dom0 has more weight than the domUs, so that it is
>> able
>> > to process the IO requests?
>> >
>> > See: http://wiki.xensource.com/xenwiki/XenBestPractices
>> >
>> > -- Pasi
>> >
>> >
>>
>> yes, the box has 8 physical cores, and the domU test installation only
>> uses two of them
>>
>
> How many cores does dom0 have?
> Did you set up the xen credit scheduler weights?
> Did you pin the vcpus to specific cores?
>
> What does "iostat 1" show in dom0 while you run the test?
> What does "xm top" show in dom0 while you run test?
>
> -- Pasi
>
>


here is the output: http://pastebin.com/c3JqU7e4

everything looks normal in my opinion


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