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    SubjectRe: raid is dangerous but that's secret (was Re: [patch] ext2/3:
    Actually, there is something the file system can do to make journaling
    safe on degraded RAIDs: make the (checksummed) journal blocks equal to
    the RAID stripe size. Or, equivalently, pad out to the RAID stripe
    size each commit.

    This sometimes leads to awkward block sizes, but while writing
    to any *one* stripe on a degraded RAID-5 endangers the others, you
    can write to *all* of them with the usual semantics.

    That's something that's a good idea for performance anyway, so maybe
    ext[34] should be more vociferous about it. E.g. check each mount
    and warn if the journal is mis-sized. Or even change the journal
    bock size on mount if it starts empty.

    The other solution, of course, is RAID-1, which I like to use for
    performance and simplicity reasons anyway. (It's really something
    of a degenerate case of the RAID-[456] rule.)

    That's one thing I really like about ZFS: its policy of "don't trust
    the disks." If nothing else, simply telling you "your disks f*ed up,
    and I caught them doing it", instead of the usual mysterious corruption
    detectec three months later, is tremendoudly useful information.

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      Last update: 2009-08-31 03:03    [W:0.018 / U:43.880 seconds]
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