linux-ext4 - Re: mdadm software raid + ext4, capped at ~350MiB/s limitation/bug?

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Date:	Sun, 28 Feb 2010 15:03:00 -0500 (EST)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Bill Davidsen <davidsen@....com>
cc:	Mike Snitzer <snitzer@...il.com>, Neil Brown <neilb@...e.de>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	linux-ext4@...r.kernel.org, Alan Piszcz <ap@...arrain.com>
Subject: Re: mdadm software raid + ext4, capped at ~350MiB/s
 limitation/bug?



On Sun, 28 Feb 2010, Bill Davidsen wrote:

> Justin Piszcz wrote:
>> 
>> 
>> On Sun, 28 Feb 2010, Mike Snitzer wrote:
>> 
>>> On Sun, Feb 28, 2010 at 4:45 AM, Justin Piszcz <jpiszcz@...idpixels.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.
>> 
>> -- 
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>> 
> I'm going to have to do some testing now, I just tested ext4 against the raw 
> speed of the device (single device test) and they were quite close to 
> identical. I'm going to order one more drive to bring my test setup up to 
> five devices, and do some testing on how it behaves.
>
> More later.

Thanks, let me know how it goes, I see the same thing, on a single hard 
drive, there is little difference between EXT4 and XFS:
http://permalink.gmane.org/gmane.linux.kernel/955357

However, when multiple disks are involved, it is a different story.

Justin.
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