If you would like to find out which tape(s) were used for a specific backup, you can use the bpimagelist command.
bpimagelist -U -client
For example, if your client was named myclient.mydomain.com and you wanted to search for backups from January 1, 2011 at 12:00 PM and January 2, 2011 at 12:00 PM, you would run the command as follows:
bpimagelist -U -client myclient.mydomain.com -d 01/01/2011 12:00:00 -e 01/02/2011 12:00:00 -media
The resulting output will be:
Media ID Last Written Server
——– —————- ———-
300047 01/02/2011 01:47 nbumaster.mydomain.com