From: Brad Campbell <brad@wasp.net.au>
To: Daniel Pittman <daniel@rimspace.net>
Cc: linux-raid@vger.kernel.org
Subject: Re: Raid-0 speed
Date: Thu, 26 Aug 2004 13:54:35 +0400 [thread overview]
Message-ID: <412DB35B.7090802@wasp.net.au> (raw)
In-Reply-To: <87k6vneok0.fsf@enki.rimspace.net>
Daniel Pittman wrote:
>>With the raid-0 running, doing a dd if=/dev/md1 of=/dev/null I get about
>> 55MB/s read speed.
>>
>>I can't quite figure out why the md is so slow. Given its using
>>streaming reads with no seeking it should be over 100MB/s.
>
>
> Your chunk size is way to low to give good streaming reads. The kernel
> needs to switch between devices every 128 kilobytes, while is rather
> low.
>
> Try slowly pushing the chunk size to 16384 and see when your performance
> gets back up to your expected level.
Nope.. Any chunk size > 4096 gives me
too big chunk_size: 8388608 > 4194303.
And the performance difference between chunk=16 and chunk=4096 is less than 5MB/s
--chunk=16 gives me 48.43 MB/s
--chunk=4096 gives me 51.52 MB/s
Regards,
Brad
next prev parent reply other threads:[~2004-08-26 9:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-08-25 5:05 Raid-0 speed Brad Campbell
2004-08-25 6:09 ` Daniel Pittman
2004-08-26 9:54 ` Brad Campbell [this message]
2004-08-26 16:41 ` Guy
2004-08-26 16:45 ` Brad Campbell
2004-08-25 17:11 ` Vladimir I. Umnov
2004-08-26 4:36 ` Brad Campbell
2004-08-27 23:35 ` Guy
2004-08-28 0:05 ` Neil Brown
2004-08-28 2:38 ` Guy
2004-08-28 4:27 ` Mikael Abrahamsson
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