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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.
    >>
    >> --
    >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
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    >> More majordomo info at http://vger.kernel.org/majordomo-info.html
    >>
    > 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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