At LSF this year, we had a discussion about error handling and in particular the problem that SCSI midlayer error handling waits for the entire SCSI host (HBA) to quiesce before it starts to abort commands etc.
James made the suggestion that FC should handle things the way SAS does, because SAS has a strategy handler that does things the right way. However, now that I finally sit down and look at the code, I don't see how this is the case. It seems inherent in the way that scsi_eh_scmd_add() and the thread in scsi_error_handler() work (in particular the strategy handler can't even be called until host_failed == host_busy; we don't bump host_failed without SHOST_RECOVERY set, which stops queueing commands to any devices attached to the whole HBA). James, am I understanding your suggestion properly? If so can you explain what you meant about the libsas code -- I see that it has its own strategy handler but as I said before we've already stopped every device attached to the HBA before we ever get there. To recapitulate the problem here, we might have a whole fabric attached to an HBA via SAS or FC, and be doing 500K IOPS happily to 50 devices. Then a single LUN goes wonky and all the IO stops while we try to recover that single device, which might take minutes. I know this has been discussed before, but can we find a way forward here? Is there some way we can start with per-device error recovery and avoid disrupting IO that we can see is working fine? Thanks, Roland -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
