Hi Chandra, Chandra Seetharaman wrote: > Hannes, > > I think we need to revisit the priority value we provide for preferred > path(4) relative to active path (2) and non-preferred(1). > > Consider the following scenario: > > Access to a lun thru 2 preferred and 2 non-preferred path. Lets call > path group with preferred paths as pg1 and with non-preferred paths as > pg2. > > Initially pg1 has priority of 8 and pg2 has priority of 2. pg1 is chosen > and I/O goes thru pg1, all good. > > Both the paths in pg1 fails, pg2 has been made the active path group and > I/O is sent thru that path and since it became "active", its priority > raises to 6 ( 2 path times (active + non-preferred)). > > When one of the paths in pg1 comes back, one would expect the failback > to happen. It doesn't happen as pg1's priority (4) is smaller than that > of pg2 (6). Which is not correct. > Is this really a valid case? This means we'll have a setup like this: rdac pg1 sda failed sdb failed pg2 sdc active sdd active Correct? So, given your assumptions, the proposed scenario would be represented like this: rdac pg1 sda active sdb failed pg2 sdc active sdd active So it is really a good idea to switch paths in this case? The 'sdb' path would not be reachable here, so any path switch command wouldn't have been received, either. I'm not sure _what_ is going to happen when we switch paths now and sdb comes back later; but most likely the entire setup will be messed up then: sda (pref & owned) 6 sdb 0 sdc (sec) 1 sdd (sec & owned) 3 and we'll be getting the path layout thoroughly jumbled then. So I don't really like this idea. We should only be switching paths when _all_ paths of a path group become available again. Providing not all paths have failed in the active group, of course. Then we should be switching paths regardless. 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
