Messages in this thread |  | | Date | Sat, 21 Mar 2009 11:20:21 -0400 | From | Mark Lord <> | Subject | Re: Overagressive failing of disk reads, both LIBATA and IDE |
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James Bottomley wrote: > On Sat, 2009-03-21 at 10:55 -0400, Mark Lord wrote: .. >> The patch *does* use the disk supplied data about the error, >> and returns success for sectors up to that point. Where it differs >> from mainline SCSI, is that it then continues attempting the remaining >> 2000 sectors (or whatever) of the request, hoping that not all of >> them are bad. > > Um, but so does SCSI without your patch ... that was my point. ..
Does it? I thought it still just failed everything after the first bad sector? Kudos are due if that's working now.
.. > I don't really think we'd do that. The problem, as you say is request > combination. I think if we really wanted to do this, we'd have block do > it. Each separate request that's merged gets a separate bio, and block > already has capabilities to pick up per bio errors, so we'd do the > partial completion of the failing bio then skip to the next one in the > request to try. That would completely solve both readahead problems and > request merging ones. ..
Yeah, that's a reasonable way to tackle. And you're right, we *did* discuss this back two years ago. It just never made it as far as new code. :)
Something else that might be good here, would be to have the md layer pass down a (per-bio?) flag indicating whether it has redundacy capability or not for the I/O. Eg. healthy RAID1/4/5/10 etc.. would set the flag, and SCSI could then just abort immediately on a bad sector, with NO retries beyond the first bad one.
On RAID0, or a degraded (no spares) RAID1 etc, it would not set the flag, so SCSI would try harder to recover the data, as we're discussing above.
This sounds like FAST_FAIL, but is different. And the hint needs to come from the upper layer that is performing redundancy.
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