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Re: [Xen-users] Massive iowait with Xen 3.2

To: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Subject: Re: [Xen-users] Massive iowait with Xen 3.2
From: Christopher Chen <muffaleta@xxxxxxxxx>
Date: Wed, 29 Apr 2009 11:15:12 -0700
Cc: Antoine Benkemoun <antoine.benkemoun@xxxxxxxxx>, Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
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Also, if you're using file: vbd access, and you're low on ram, I
imagine your buffer cache on the dom0 is nearly nonexistent, which
would kill any writes.

You might want to get more RAM while you're at it.

On Tue, Apr 28, 2009 at 6:20 AM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
> On Tue, Apr 28, 2009 at 7:59 PM, Antoine Benkemoun
> <antoine.benkemoun@xxxxxxxxx> wrote:
>> Thank you for your answer. Sorry for the headers !
>> 4MB/s read speed is just plain ridiculous for a hard drive or is it just me
>> ?
> I don't think its the transfer rate. Its the IOPS thats causing your problems.
> This link (from Googling "one disk iops")
> http://forums11.itrc.hp.com/service/forums/questionanswer.do?admit=109447626+1240923773781+28353475&threadId=1122630
> indicates max IOPS for one disk is lower then your current numbers
> (180). So I guess you're IOPS bound. Adding more disk with the right
> setup would increase the number of IOPS you can handle.
> Since the IOPS are mostly read, you MIGHT be able to reduce it by
> giving domU more RAM, enough to hold the torrent it's running. So
> instead of having 8 domUs with 256 MB each, try using only 1 or 2
> domUs with 1 GB memory.
>> These domains are actually stored on LVM so that's already in place but
>> iostat doesn't seem to differenciate...
> Weird. I swear in shows up on RHEL. Could be they have vendor-specific
> patch. What does /proc/partitions and /proc/diskstats show, does it
> have "dm" entries?
> Anyway, from the output of "xm top" you should also be able to
> determine which domU uses most I/O (look in VBD_RD column). In general
> bittorrent IS very I/O intensive. If you want to limit the amount of
> I/O a domU can use (so that whatever they do they never made the
> entire system crawl down), you might be interested in dm-ioband.
> Haven't used it myself, but it looks good.
> http://people.valinux.co.jp/~ryov/dm-ioband/
> Regards,
> Fajar
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Chris Chen <muffaleta@xxxxxxxxx>
"I want the kind of six pack you can't drink."
-- Micah

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