Messages in this thread | | | Date | Fri, 02 Feb 2007 11:16:19 -0500 | From | Ric Wheeler <> | Subject | Re: [PATCH] scsi_lib.c: continue after MEDIUM_ERROR |
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James Bottomley wrote: > On Fri, 2007-02-02 at 14:42 +0000, Alan wrote: > >>> The interesting point of this question is about the typically pattern of >>> IO errors. On a read, it is safe to assume that you will have issues >>> with some bounded numbers of adjacent sectors. >>> >> Which in theory you can get by asking the drive for the real sector size >> from the ATA7 info. (We ought to dig this out more as its relevant for >> partition layout too). >>
Actually, my point is that damage typically impacts a cluster of disk sectors that are adjacent. Think of a drive that has junk on the platter or a some such thing - the contamination is likely to be localized. >> >>> I really like the idea of being able to set this kind of policy on a per >>> drive instance since what you want here will change depending on what >>> your system requirements are, what the system is trying to do (i.e., >>> when trying to recover a failing but not dead yet disk, IO errors should >>> be as quick as possible and we should choose an IO scheduler that does >>> not combine IO's). >>> >> That seems to be arguing for a bounded "live" time including retry run >> time for a command. That's also more intuitive for real time work and for >> end user setup. "Either work or fail within n seconds" >> > > Actually, then I think perhaps we use the allowed retries for this ... > I really am not a big retry fan for most modern drives - the drive will try really, really hard to complete an IO for us and multiple retries can just slow down the higher level application from recovering. > So you would fail a single sector and count it against the retries. > When you've done this allowed retries times, you fail the rest of the > request. > > James > > I think that we need to play with some of these possible solutions on some real-world bad drives and see how they react.
We should definitely talk more about this at the workshop ;-)
ric
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