From mboxrd@z Thu Jan  1 00:00:00 1970
From: Justin Piszcz <jpiszcz@lucidpixels.com>
Subject: Re: mdadm software raid + ext4, capped at ~350MiB/s
 limitation/bug?
Date: Sun, 28 Feb 2010 10:03:04 -0500 (EST)
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To: Mike Snitzer <snitzer@gmail.com>
Cc: Bill Davidsen <davidsen@tmr.com>, Neil Brown <neilb@suse.de>, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, Alan Piszcz <ap@solarrain.com>
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On Sun, 28 Feb 2010, Mike Snitzer wrote:

> On Sun, Feb 28, 2010 at 4:45 AM, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:

[ .. ]

>
> How did you format the ext3 and ext4 filesystems?
>
> Did you use mkfs.ext[34] -E stride and stripe-width accordingly?
> AFAIK even older versions of mkfs.xfs will probe for this info but
> older mkfs.ext[34] won't (though new versions of mkfs.ext[34] will,
> using the Linux "topology" info).

Yes and it did not make any difference:
http://lkml.org/lkml/2010/2/27/77

Incase anyone else wants to try too, you can calculate by hand, or if you
are in a hurry, I found this useful:
http://busybox.net/~aldot/mkfs_stride.html

I believe there is something fundamentally wrong with ext4 when performing 
large sequential I/O when writing, esp. after Ted's comments.

Justin.