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    md: Don't update ->recovery_offset when reshaping an array to fewer devices. · 70fffd0b
    NeilBrown 提交于
    When an array is reshaped to have fewer devices, the reshape proceeds
    from the end of the devices to the beginning.
    
    If a device happens to be non-In_sync (which is possible but rare)
    we would normally update the ->recovery_offset as the reshape
    progresses. However that would be wrong as the recover_offset records
    that the early part of the device is in_sync, while in fact it would
    only be the later part that is in_sync, and in any case the offset
    number would be measured from the wrong end of the device.
    
    Relatedly, if after a reshape a spare is discovered to not be
    recoverred all the way to the end, not allow spare_active
    to incorporate it in the array.
    
    This becomes relevant in the following sample scenario:
    
    A 4 drive RAID5 is converted to a 6 drive RAID6 in a combined
    operation.
    The RAID5->RAID6 conversion will cause a 5 drive to be included as a
    spare, then the 5drive -> 6drive reshape will effectively rebuild that
    spare as it progresses.  The 6th drive is treated as in_sync the whole
    time as there is never any case that we might consider reading from
    it, but must not because there is no valid data.
    
    If we interrupt this reshape part-way through and reverse it to return
    to a 5-drive RAID6 (or event a 4-drive RAID5), we don't want to update
    the recovery_offset - as that would be wrong - and we don't want to
    include that spare as active in the 5-drive RAID6 when the reversed
    reshape completed and it will be mostly out-of-sync still.
    Signed-off-by: NNeilBrown <neilb@suse.de>
    70fffd0b
raid5.c 164.9 KB