Re: try to write back redundant data before failing disk in raid5 setup

[Dick Snippe <Dick.Snippe@tech.omroep.nl>]

On Mon, May 01, 2006 at 01:17:42AM +0200, Dick Snippe wrote:

> Suppose a read action on a disk which is member of a raid5 (or raid1 or any
> other raid where there's data redundancy) fails.
> What ahppens next is that the entire disk is marked as "failed" and a raid5
> rebuild is initiated.
>
> However, that seems like overkill to me. If only one sector on one disk
> failed, that sector could be re-calculated  (using parity calculations)
> AND written back to the original disk (i.e. the disk with the bad sector).
> Any modern disk will do sector remapping, so the bad sector will simply be
> replaced by a good one and there's no need to fail the entire disk.

Sigh. Just checked the kernel source. Recent 2.6 kernels (>= 2.6.15) appear
to have support for this (See raid5_end_read_request in drivers/md/raid5.c).
Earlier versions don't.

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