Hi Hannes, (10/18/10 20:55), Hannes Reinecke wrote: >> Does 'retryable' of EIO mean retryable in multipath layer? >> If so, what is the difference between EIO and ENOLINK? >> > Yes, EIO is intended for errors which should be retried at the > multipath layer. This does _not_ include transport errors, which are > signalled by ENOLINK. > > Basically, ENOLINK is a transport error, and EIO just means > something is wrong and we weren't able to classify it properly. > If we were, it'd be either ENOLINK or EREMOTEIO. > >> I've heard of a case where just retrying within path-group is >> preferred to (relatively costly) switching group. >> So, if EIO (or other error code) can be used to indicate such type >> of errors, it's nice. >> > Yes, that was one of the intention. Great to hear that. And when it comes to retrying, the next problem is who controls it. I don't think it's good to duplicate retry logic in multipath and underlying device like SCSI (i.e. sd retries 5 times). So perhaps we need a way to disable (or limit) retries in underlying device at least. >> Also (although this might be a bit off topic from your patch), >> can we expand such a distinction to what should be logged? >> Currently, it's difficult to distinguish important SCSI/block errors >> and less important ones in kernel log. >> For example, when I get a link failure on sda, kernel prints something >> like below, regardless of whether the I/O is recovered by multipathing or not: >> end_request: I/O error, dev sda, sector XXXXX >> > Indeed, when using the above we could be modifying the above > message, eg by > > end_request: transport error, dev sda, sector XXXXX > > or > > end_request: target error, dev sda, sector XXXXX > > which would improve the output noticeable. It improves but still they look like critical errors even if multipath saves them. When I see this: end_request: target error, dev sda, sector XXXXX I can't tell whether it's a real error visible to user space or it's just recoverred by multipath retry/failover afterwards. >> Setting REQ_QUIET in dm-multipath could mask the message >> but also other important ones in SCSI. >> > Hmm. Not sure about that, but I think the above modifications will > be useful already. > > I'll be sending an updated patch. Thank you. I'm looking for that. -- Jun'ichi Nomura, NEC Corporation -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
