From: Bill Davidsen <davidsen@tmr.com>
To: Mark Hahn <hahn@mcmaster.ca>
Cc: Neil Brown <neilb@suse.de>, Tomka Gergely <gergely@tomka.hu>,
linux-raid@vger.kernel.org
Subject: Re: sw raid0 read bottleneck
Date: Wed, 14 Mar 2007 13:41:14 -0500 [thread overview]
Message-ID: <45F841CA.8040704@tmr.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0703131711220.28796@coffee.psychology.mcmaster.ca>
Mark Hahn wrote:
>> 15 drives and 64K chunks gives 960K per stripe.
>> The raid0 code should set the read-ahead to twice that: 1920K
>> which I would have thought would be enough, but apparently not.
>
> choosing the RA size should depend in some way on speed, shouldn't it?
> after all, the goal is to have enough reads queued to avoid a "stall"
> while un-read-ahead-ed sectors pass under the head. for a typical
> 60 MB/s, 7200 rpm disk, a track is .5 MB. the heuristic above only reads
> ahead .12 MB...
While I'm sure you realize it, some reader won't, so I'll point out that
a cylinder is all the tracks which can be read without a seek, and
cylinder size is track size times number of data heads. If you want max
speed you can read that much off a drive at a time...
--
bill davidsen <davidsen@tmr.com>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
next prev parent reply other threads:[~2007-03-14 18:41 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-13 16:23 sw raid0 read bottleneck Tomka Gergely
2007-03-13 16:48 ` Justin Piszcz
2007-03-13 17:34 ` Tomka Gergely
2007-03-13 18:15 ` Tomka Gergely
2007-03-13 18:42 ` Justin Piszcz
2007-03-13 20:51 ` Neil Brown
2007-03-13 21:09 ` Tomka Gergely
2007-03-13 21:29 ` Mark Hahn
2007-03-14 18:41 ` Bill Davidsen [this message]
2007-03-14 19:32 ` Mark Hahn
2007-03-14 21:53 ` Bill Davidsen
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