Ric Wheeler 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.. >> >> Definitely an improvement. >> >> The number of retries is an entirely separate issue. >> If we really care about it, then we should fix SD_MAX_RETRIES. >> >> The current value of 5 is *way* too high. It should be zero or one. >> >> Cheers >> > I think that drives retry enough, we should leave retry at zero for > normal (non-removable) drives. Should this be a policy we can set like > we do with NCQ queue depth via /sys ? The transport might also want a say. I see ABORTED COMMAND errors often enough with SAS (e.g. due to expander congestion) to warrant at least one retry (which works in my testing). SATA disks behind SAS infrastructure would also be susceptible to the same "random" failures. Transport Layer Retries (TLR) in SAS should remove this class of transport errors but only SAS tape drives support TLR as far as I know. Doug Gilbert > We need to be able to layer things like MD on top of normal drive errors > in a way that will produce a system that provides reasonable response > time despite any possible IO error on a single component. Another case > that we end up doing on a regular basis is drive recovery. Errors need > to be limited in scope to just the impacted area and dispatched up to > the application layer as quickly as we can so that you don't spend days > watching a copy of huge drive (think 750GB or more) ;-) > > ric - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
