Re: end to end error recovery musings

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Theodore Tso wrote:
Can someone with knowledge of current disk drive behavior confirm that
for all drives that support bad block sparing, if an attempt to write
to a particular spot on disk results in an error due to bad media at
that spot, the disk drive will automatically rewrite the sector to a
sector in its spare pool, and automatically redirect that sector to
the new location.  I believe this should be always true, so presumably
with all modern disk drives a write error should mean something very
serious has happend.


This is what will /probably/ happen. The drive should indeed find a spare sector and remap it, if the write attempt encounters a bad spot on the media.

However, with a large enough write, large enough bad-spot-on-media, and a firmware programmed to never take more than X seconds to complete their enterprise customers' I/O, it might just fail.


IMO, somewhere in the kernel, when we receive a read-op or write-op media error, we should immediately try to plaster that area with small writes. Sure, if it's a read-op you lost data, but this method will maximize the chance that you can refresh/reuse the logical sectors in question.

	Jeff


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