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    SubjectRe: Why does the md/raid subsystem does not remap bad sectors in a raid array?
    There are a few reasons but my guess is this: md tries to use the
    entire available storage (of the smallest element) in a given set of
    devices, which means there is no room for remappery.

    However, if MD could be told to set aside some percentage of this
    value, or some fixed amount (like, say, 10MB) then the *possibility*
    of remapping blocks becomes possible.

    However, to add this functionality one would have to consider the following:

    1. how much to set aside?
    2. where? beginning, end, middle, staggered in chunks?
    3. how to tell MD that block A maps to block B on device C? Should it
    be done as an exception list (all blocks not in list X refer to their
    actual block, otherwise they refer to a redirected block)? or as a
    direct map (or something else)?

    Perhaps an alternative would be to add a new block layer which takes
    an existing block device X and exposes a new, automatic block
    remapper-y block device Y (bad reads might continue to return errors
    but writes to a previous bad read might go to a new block and so would
    subsequent reads) and so on.

    Perhaps the easiest way to test this would be to hack NBD or AoE and
    build a raid out of such devices.

    Just ramblin' here.


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      Last update: 2008-11-23 01:15    [W:0.019 / U:0.052 seconds]
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