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    SubjectRe: limits on raid
    On Sun, 17 Jun 2007, Wakko Warner wrote:

    > dean gaudet wrote:
    > > On Sat, 16 Jun 2007, Wakko Warner wrote:
    > >
    > > > When I've had an unclean shutdown on one of my systems (10x 50gb raid5) it's
    > > > always slowed the system down when booting up. Quite significantly I must
    > > > say. I wait until I can login and change the rebuild max speed to slow it
    > > > down while I'm using it. But that is another thing.
    > >
    > > i use an external write-intent bitmap on a raid1 to avoid this... you
    > > could use internal bitmap but that slows down i/o too much for my tastes.
    > > i also use an external xfs journal for the same reason. 2 disk raid1 for
    > > root/journal/bitmap, N disk raid5 for bulk storage. no spindles in
    > > common.
    > I must remember this if I have to rebuild the array. Although I'm
    > considering moving to a hardware raid solution when I upgrade my storage.

    you can do it without a rebuild -- that's in fact how i did it the first

    to add an external bitmap:

    mdadm --grow --bitmap /bitmapfile /dev/mdX

    plus add "bitmap=/bitmapfile" to mdadm.conf... as in:

    ARRAY /dev/md4 bitmap=/bitmap.md4 UUID=dbc3be0b:b5853930:a02e038c:13ba8cdc

    you can also easily move an ext3 journal to an external journal with
    tune2fs (see man page).

    if you use XFS it's a bit more of a challenge to convert from internal to
    external, but see this thread:

    i found that i had to do "sb 1", "sb 2", ..., "sb N" for all sb rather
    than just the "sb 0" that email instructed me to do.

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      Last update: 2007-06-17 19:33    [W:0.021 / U:17.668 seconds]
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