Re: [PATCH] scsi_lib.c: continue after MEDIUM_ERROR

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Jeff Garzik wrote:
Mark Lord wrote:
Eric D. Mudama wrote:

Actually, it's possibly worse, since each failure in libata will generate 3-4 retries. With existing ATA error recovery in the drives, that's about 3 seconds per retry on average, or 12 seconds per failure. Multiply that by the number of blocks past the error to complete the request..

It really beats the alternative of a forced reboot
due to, say, superblock I/O failing because it happened
to get merged with an unrelated I/O which then failed..
Etc..


FWIW -- speaking generally -- I think there are inevitable areas where libata error handling combined with SCSI error handling results in suboptimal error handling.

Just creating a list of "<this behavior> should be handled <this way>, but in reality is handled in <this silly way>" would be very helpful.

I agree - Tejun has done a great job at giving us a great base. Next step is to get clarity on what the types of errors are and how to differentiate between them (and maybe how that would change by class of device?).


Error handling is tough to get right, because the code is exercised so infrequently. Tejun has actually done an above-average job here, by making device probe, hotplug and other "exceptions" go through the libata EH code, thereby exercising the EH code more than one might normally assume.

Some errors in libata probably should not be retried more than once, when we have a definitive diagnosis. Suggestions for improvements are welcome.

    Jeff

One thing that we find really useful is to inject real errors into devices. Mark has some patches that let us inject media errors, we also bring back failed drives and run them through testing and occasionally get to use analyzers, etc to inject odd ball errors.

Hopefully, we will get some time to brainstorm about this at the workshop,

ric
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