Alan wrote:

quoted

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).

quoted

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"

Which is more or less the "streaming" feature set in recent
ATA standards. [Alas, streaming and NCQ/TCQ can't be done
with the same access.] SCSI has its Read Write Error Recovery
mode page which doesn't have timeouts but does have Read
and Write Retry Counts amongst other fields that control
the amount (and indirectly the time) of attempted error
recovery.

Doug Gilbert