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

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

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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