RE: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

[Adam Radford <aradford@3WARE.com>]

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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