John,

Assuming the device(s) that your primary copies are on and working correctly
you should be able to issue the command
 vary on <volume name> which will cause TSM to place the device online and
start a copy from the mirror and get everything synchronized again.

Just went through this.... In our case we lost the device for one of the
primary dbvol's. Mirrors worked like a champ and saved the DB!

Curt Magura
Lockheed Martin EIS
Gaithersburg, Md.
301-240-6305