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Re: poor io performance with xfs+raid5

To: Steve Lord <lord@xxxxxxx>
Subject: Re: poor io performance with xfs+raid5
From: Mike Eldridge <diz@xxxxxxxxx>
Date: Thu, 25 Apr 2002 15:41:35 -0500
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <1019765945.12905.102.camel@jen.americas.sgi.com>; from lord@sgi.com on Thu, Apr 25, 2002 at 03:19:05PM -0500
References: <Pine.BSO.4.44.0204251216360.25324-100000@paperboy.websocietyinc.com> <3CC85999.501431E5@ch.sauter-bc.com> <20020425144025.N16048@ornery.cafes.net> <1019765945.12905.102.camel@jen.americas.sgi.com>
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On Thu, Apr 25, 2002 at 03:19:05PM -0500, Steve Lord wrote:
> Well, Duh! I should have seen that first time around, I get into the
> habit of reading my email too fast!
> 
> We may be able to fix some things, if we can remake the filesystem.
> First you need to know the stripe unit of your raid - we can feed
> this into XFS to make it do stripe aligned allocations. This has
> to be done by hand on linux. Take a look at the mkfs.xfs man page
> and the section on sunit and swidth options. Probably bump your log size
> up from the default somewhat, not sure how it ended up as 1839
> that is scary.

RAID5 on this card offers only a 64K stripe size.  however, i will be
recreating the array as RAID1 or RAID10, which offers stripe sizes from
64K to 1MB.  i'm not sure which is the best way to go.  i think that the
best thing to do, considering additonal space requirements might be
neccessary, is to go with multiple RAID1 arrays and let LVM do the
striping.  any caveats here?

this particular box is a mail server and it handles a lot of i/o with
pretty small files (< 64K).  i want to optimize for performance.
unfortunately, this is also my *first* foray into xfs/lvm/raid, so i
want to make sure i have as much information as possible before i carve
it all in stone.

i need to go read some more about LVM...

as for the log, yeah, just over 7MB, i have no idea either.  info i have
read suggests a 32MB log, but i'd like to use something bigger, perhaps
128MB.  any caveats to using a log of this size?

> You still have not said which kernel version you are running beyond 2.4,
> unless I speed read over that too.

i did in a previous email.  :)

it's vanilla 2.4.18 with the xfs-1.1 release patches applied.

-mike

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