Messages in this thread | | | From | Neil Brown <> | Date | Tue, 4 Dec 2007 13:46:19 +1100 | Subject | Is BIO_RW_FAILFAST really usable? |
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I've been looking at use BIO_RW_FAILFAST in md/raid to improve handling of some error cases.
This is particularly significant for the DASD driver (s390 specific). I believe it uses optic fibre to connect to the drives. When one of these paths is unplugged, IO requests will block until an operator runs a command to reset the card (or until it is plugged back in). The only way to avoid this blockage is to use BIO_RW_FAILFAST. So we really need BIO_RW_FAILFAST for a reliable RAID1 configuration on DASD drives.
However, I just tested BIO_RW_FAILFAST on my SATA drives: controller
02:06.0 RAID bus controller: Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] Serial ATA Controller (rev 02)
(not using the cards minimal RAID functionality) and requests fail immediately and always with e.g.
sd 2:0:0:0: [sdc] Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK,SUGGEST_OK end_request: I/O error, dev sdc, sector 2048
So fail fast obviously isn't generally usable.
What is the answer here? Is the Silicon Image driver doing the wrong thing, or is DASD doing the wrong thing, or is BIO_RW_FAILFAST under-specified and we really need multiple flags or what?
Any ideas?
Thanks, NeilBrown
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