Hi Joe, Sorry that you will get these twice (especially considering it is so long). Mails from my cs.wisc.edu account do not arrive on dm-devel for a couple of days sometimes. I am working on adding support for IBM's fastt which has a failover mode that requires a failover command be sent before a group of paths can be used. The following patches implement the basic support needed from dm. 01-ps-failpath.patch - move the path failure decision to the path selector. Some ps's may want to select paths that have a couple failures over one that has N failures. If a ps has to track this info there didn't seem to be a compelling reason to also do it in dm-mpath.c. Well code duplication and sharing is a good reason to do it in dm-mpath. It would be nice if I could just add an init function to any ps and leach off other people's work :) but is that too modular? Additionally, if a ps fails to activate a path or cannot use it during initialization it may want to fail it. 02-export-ps-register-fns.patch - exports the register and unregister ps functions. 03-ps-init.patch - makes priority group / path-selector initialization possible. Remapping failed bios from end_io was not nice becuase you couldn't choose a path until you knew a group was activated and what paths in that group were still functional. Plus, incoming IO needed to be mapped while failures were coming in. I guess you could just make map_io sleep or do some internal queueing. I choose the former, so I had to move the remap map_io call to dispatch_failed_ios and add a get_mapinfo accessor function. I think queueing incoming io while you finish the failed may be better, but targets calling dm's queueing mechanism didn't seem right, and reimplementing it didn't either. Well, I do not know if it is better or not. While paths are failing performance is going to take a hit so io ordering may only be a problem if you are concerned with journaling or barrier type stuff (but as we end up sending IO down multiple queues we cannot gaurantee ordering on the normal IO code path anyways). 04-path-to-dev.patch - adds another accessor so path-selectors can access a path's bdev. This is necessary for devices which need to send commands down to the device. (see rdac-test-support.patch) 05-mpath-wq.patch - dispatch_failed_ios can sleep. It should not disrupt other users of the default work queue. Under heavy load or group/ps initializations on a single processor machine, this conflict becomes painful. complete-all.patch - the patches are against linux-2.6.5-rc1 udm1 which doesn't have complete_all exported. Newer mm versions do. rdac-test-support.patch - this is just an example of what needs to could be done by the ps to send a failover command to the device. This example is just sending a TUR, and I just bascially ripped off the rr ps's other functions. The point is that I have to inject a command into a queue using blk_execute_rq or elv_add_request. Mike