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    SubjectRe: How to handle >16TB devices on 32 bit hosts ??
    On Sat, Jul 18, 2009 at 02:52:13AM -0400, Andreas Dilger wrote:
    > If you aren't running a 32-bit system with this config, you shouldn't
    > really care. For those systems that need to run in this mode they
    > would rather have it work a few percent slower instead of not at all.

    Well, it doesn't work at all anyways due to the fsck problem.

    > The last test numbers I saw were 5GB of RAM for a 20TB filesystem,
    > but since the bitmaps used are fully-allocated arrays that isn't
    > surprising. We are planning to replace this with a tree, since the
    > majority of bitmaps used by e2fsck have large contiguous ranges of
    > set or unset bits and can be represented much more efficiently.

    You would need to get <~2.5GB for 32bit. In practice that's
    the limit you have there.

    > Also, for filesystems like btrfs or ZFS the checking can be done
    > online and incrementally without storing a full representation of
    > the state in memory.

    You could, but I suspect it would be cheaper to just use a
    64bit system than to rewrite fsck. 64bit is available
    for a lot of embedded setups these days too.

    -Andi

    --
    ak@linux.intel.com -- Speaking for myself only.


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