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SubjectRe: 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@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.
>>
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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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