(1) When I change the multipath config file to blacklist an already multipathed block device, I must first remove that device from the active multipath configuration via "multipath -F" or "dmsetup remove <map-name>" then run "multipath". Seems like I should not have to do all of this. A simple invocation of "multipath" after modifying the multipath configuration file should do it instead by checking the current configuration and removing/closing the mapped device for me if that device is currently in the active multipath configuration. Also, don't we need a multipath(8) capability to remove a specific multipath mapped device from the active configuration? (2) This isn't even sufficient since the multipathd holds an open on each multipath mapped device. One result of this is that the target devices used by the mapped device are not available for use by any application which must "claim" them exclusively, for example, mount(8) or for use via raw io. I must kill multipathd before I can use any of the target devices by these "claiming" applications. Seems like multipath should get multipathd to close its open on the newly blacklisted block device. (3) After experimenting with this stuff on my SuSE SLES 9 SP2 host, while trying to run performance tests I got myself into a situation where a multipath mapped device file referred to THE WRONG LU. I had no idea this was happening until I researched why dd(1) was writing only half the number of 4kb records to the LU than was a dd(1) to the native scsi device path. This happened because it appears that symbolic links in /dev/disk/by-name to device mapper device files in /dev are NOT cleaned up as a result of running "multipath -F", "dmsetup remove <map-name>, or "dmsetup remove_all". A subsequent invocation of multipath will not necessarily assign multipath mapped devices to the same device mapper minor instances (for example, if one or more of them are blacklisted after the remove step) causing the stale symbolic links in /dev/disk/by-name to refer to the wrong dm-<minor> device file in /dev. An invocation of "multipath -F" did cleanup device files in /dev on my Red Hat AS 4 host but an invocation of "dmsetup remove <map-name>" did not. I was loath to experiment with "dmsetup remove_all" on my Red Hat host since my root device on that host is on a device mapper LVM2 logical volume. Otherwise, I suspect that this command would fail to clean up device files in the same way "dmsetup remove_all" failed.
