On 10/18/2010 10:09 AM, Jun'ichi Nomura wrote: > Hi Hannes, > > Thank you for working on this issue and sorry for very late reply... > > (08/30/10 23:52), Hannes Reinecke wrote: >> From: Hannes Reinecke <hare@xxxxxxx> >> Date: Mon, 30 Aug 2010 16:21:10 +0200 >> Subject: [RFC][PATCH] scsi: Detailed I/O errors >> >> Instead of just passing 'EIO' for any I/O errors we should be >> notifying the upper layers with some more details about the cause >> of this error. >> This patch updates the possible I/O errors to: >> >> - ENOLINK: Link failure between host and target >> - EIO: Retryable I/O error >> - EREMOTEIO: Non-retryable I/O error >> >> 'Retryable' in this context means that an I/O error _might_ be >> restricted to the I_T_L nexus (vulgo: path), so retrying on another >> nexus / path might succeed. > > 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. > > 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. > 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. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Markus Rex, HRB 16746 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
