On Mon, Aug 23 2010 at 8:14am -0400, Tejun Heo <tj@xxxxxxxxxx> wrote: > Hello, > > On 08/20/2010 10:26 AM, Kiyoshi Ueda wrote: > > I think that's correct and changing the priority of DM_ENDIO_REQUEUE > > for REQ_FLUSH down to the lowest should be fine. > > (I didn't know that FLUSH failure implies data loss possibility.) > > At least on ATA, FLUSH failure implies that data is already lost, so > the error can't be ignored or retried. > > > But the patch is not enough, you have to change target drivers, too. > > E.g. As for multipath, you need to change > > drivers/md/dm-mpath.c:do_end_io() to return error for REQ_FLUSH > > like the REQ_DISCARD support included in 2.6.36-rc1. > > I'll take a look but is there an easy to test mpath other than having > fancy hardware? It is easy enough to make a single path use mpath. Just verify/modify /etc/multipath.conf so that your device isn't blacklisted. multipathd will even work with a scsi-debug device. You obviously won't get path failover but you'll see the path get marked faulty, etc. > > By the way, if these patch-set with the change above are included, > > even one path failure for REQ_FLUSH on multipath configuration will > > be reported to upper layer as error, although it's retried using > > other paths currently. > > Then, if an upper layer won't take correct recovery action for the error, > > it would be seen as a regression for users. (e.g. Frequent EXT3-error > > resulting in read-only mount on multipath configuration.) > > > > Although I think the explicit error is fine rather than implicit data > > corruption, please check upper layers carefully so that users won't see > > such errors as much as possible. > > Argh... then it will have to discern why FLUSH failed. It can retry > for transport errors but if it got aborted by the device it should > report upwards. Yes, we discussed this issue of needing to train dm-multipath to know if there was a transport failure or not (at LSF). But I'm not sure when Hannes intends to repost his work in this area (updated to account for feedback from LSF). > Maybe just turn off barrier support in mpath for now? I think we'd prefer to have a device fail rather than jeopardize data integrity. Clearly not ideal but... -- 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
