On Wed, Jan 14, 2004 at 01:36:49PM -0600, Kevin Corry wrote: > Hi, > > I just had a couple questions about the overall design and direction of the DM > multipath module. > > 1. Priority Groups. > > DM-multipath allows paths to be placed in groups, with each group assigned a > priority (0 to 1024). What is the intended purpose for these groups? In the > current code, if a device has multiple groups, only the lowest-priority group > is used. I'm assuming this will change, but I just wanted to get an idea of > how the group priority will affect path selection. Kevin, low numbers imply high priority (ie, group with prio 1 is used before group with prio 3). What this actually comes down to is, that io gets dispatched to the group with the highest priority (lowest #) until _all_ its paths become faulty. One point to take into consideration later would be: do we want to hang on a higher priority group with just 1 path operational, _while_ we've got lower priority ones with multiple paths ? > > 2. Multipath Daemon > > The daemon's job is to resubmit failed I/Os to a different path, and to > periodically test each of the paths to see if they've failed or recovered > from failure. However, currently the daemon only wakes up on the error path > for normal I/Os. This means a path could be marked faulty, but never > reactivated if the path gets fixed. > > Obviously the daemon needs a way to wake-up periodically so it can run it's > test I/Os. The comments in dm-daemon.h say the worker function should return > a "hint" as to when they should be woken up, but currently this return value > is unused. I'm trying to look into how to implement this functionality in the > dm-daemon code, but I figured I'd ask here and see if anyone has already come > up with a plan for this. Once we get the multipath daemon to do its periodic > path-testing, I think we'll have a working prototype. Joe, is that still the case (it is supposed to wake up regularly and test io on failed paths as Kevin suggests) ? > > > Thanks! > -- > Kevin Corry > kevcorry@xxxxxxxxxx > http://evms.sourceforge.net/ > > > _______________________________________________ > > dm-devel@xxxxxxxxxxx > http://lists.sistina.com/mailman/listinfo/dm-devel -- Regards, Heinz -- The LVM Guy -- *** Software bugs are stupid. Nevertheless it needs not so stupid people to solve them *** =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Sistina Software Inc. Senior Consultant/Developer Am Sonnenhang 11 56242 Marienrachdorf Germany Mauelshagen@xxxxxxxxxxx +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-