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SubjectRE: File system performance, hardware performance, ext3, 3ware RA ID1, etc.
Date
Perhaps you are issuing non purely sequential IO.  The card firmware does
some
reodering, but at some point it will cause performance degradation. Can you
try
kernel 2.6 w/xfs?

Also, in my experience, the 'raw io' interface doesn't issue any
asynchronous IO. The
card _definately_ needs asynchronous IO posted to it or you will not get
good results
because you won't get all the drives busy.

-Adam

-----Original Message-----
From: Timothy Miller [mailto:miller@techsource.com]
Sent: Friday, February 13, 2004 2:57 PM
To: Daniel Blueman
Cc: linux-kernel@vger.kernel.org
Subject: Re: File system performance, hardware performance, ext3, 3ware
RAID1, etc.




Daniel Blueman wrote:
> Willy Tarreau <willy@w.ods.org> wrote in message
> news:<1oEGw-2ex-1@gated-at.bofh.it>...
>
>>On Thu, Feb 12, 2004 at 06:32:31PM -0500, Timothy Miller wrote:
>>
>>
>>>For writes, iozone found an upper bound of about 10megs/sec, which is
>>>abysmal. Typically, I'd expect writes to be faster (on a single drive)
>>>than reads, because once the write is sent, you can forget about it.
>>>You don't have to wait around for something to come back, and that
>>>latency for reads can hurt performance. The OS can also buffer writes
>>>and reorder them in order to improve efficiency.
>>
>>It depends on the disk too. Lots of disks (specially IDE) are far slower
>>on writes than they are on reads.
>
>
> No. Have you verified this? If you 'dd' your swap partition from /dev/zero
> on IDE, you'll see write performance closely matches read performance, for
> drives old and new.
>

And this sort of things is what I find with raw writes to the model of
drive I'm using. However, it seems that there must be some issue with
the 3ware 7000-2 which is killing performance, or the way the Linux
kernel is dealing with this sorta-SCSI device.

The WD1200JB should get like 30-40 megs/sec, but when being accessed
through the 3ware, I get 10-16 megs/sec.

What could the 3ware be doing?

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