On Saturday November 16, jbass@dmsd.com wrote:
> On first error the system currently appears to just abandon a drive, forcing
> the system into degraded mode for all I/O which follows. A much more reasonable
> approach would be to not abandon the drive completely, but rather build a fast
> lookup table with known bad blocks which would allow accesses to most areas of
> the array to continue without degradation, and only areas that have bad blocks
> would be forced into degraded mode.
>
> Many drives will trash a sector if power drops when writing, and that sector
> will generate read errors until written. It makes sense on those drives to
> recover the data in degraded mode, and re-write followed by a verify. If the
> verify fails, and the drive support dynamic sparing/remapping the sector
> should be remapped, rewritten, and verified again. On a large 200GB arry, this
> single feature would remove nearly a day of reconstruction time for normal
> errors and sector failures, substantially improving realized reliability.
>
> Doing dynamic error management would remove 99% of the gross software raid
> device failures I have seen over the last year.
You are largely correct...
I look forward to you providing (or sponsoring) code to do this. :-)
Maybe this should go on a FAQ as it does get mentioned from time to
time.
The answer is:
Yes, it could be done.
No, it hasn't been done.
Patches are always welcome.
NeilBrown
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