On Thu, 2009-05-07 at 16:39 -0500, Eugene Vilensky wrote:
> Right now I have backgrounded a 'vgscan -v' operation that froze,
> which has never happened before. I assume it is trying to scan the
> '/dev/mpath23' device that is supported by these four downed paths,
> and I am worried what would happen if I removed the maps manually
> while in this state.
> 
> I am surprised there is not an error-return of some kind between
> vgscan and dm-multipath if all paths for a particular mpath device are
> down...

Sounds like you multipath devices are set to "queue_if_no_path" which
basically tells the multipath layer to queue all request forever even if
there are no available paths.  You can generally free hung commands on a
device that is not coming back by setting "fail_if_no_path" on the
device with dmsetup.  The command would be something like this:

dmsetup message mpath23 0 fail_if_no_path

Once you do that the multipath layer should return errors to the hung
command and it should exit.

Here's a reference in the Redhat manuals:

http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/DM_Multipath/queueifnopath_issues.html

Once the command errors out you should be able to manually remove the
failed paths.  The "multipath -F" command should remove any unused
multipath maps, however, unused means that the VG needs to be
deactivated first.  Once you set "fail_if_no_path" you should be able to
deactivate the VG even though all paths are down.

Good luck. 

Later,
Tom


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