We have had a real headscratcher with our backups of late. The setup has the tape jukebox connected to the dual-head NetApp 3170 as an NDMP device. EMC (formerly Legato) Networker runs on a CentOS Linux box and directs the NDMP jobs on the filer. This worked just fine for months, backing up multiple volumes. Late last year we installed a new Microsoft Exchange and Enterprise Vault infrastructure with the multiple volumes exported as iSCSI LUNs to the Windows servers. This also worked fine until we configured the backup jobs.
Whatever we did the two volumes hosting the I: drives for the Vault servers just would not back up. The error message essentially said there was no backup device (tape drive) available, which was nonsense as other similar volumes in the same group were backing up just dandy.
EMC scratched their heads too.
Eventually, inspired by the Sherlock Holmes maxim that “if you eliminate the impossible, whatever is left, however improbable, must be the truth” I started mucking around with volume names. You see the I: drives hold the indexes for the Vault mailbox indexes, so we helpfully named them evmb01_indexes and evmb02_indexes. No other volumes had the string “index” embedded in their name, and that was all that differentiated them from the volumes that could find the tape drive. Improbable but true: Networker will not let you backup a volume with “index” in its name to an NDMP device.

Following up with EMC this is a deliberate feature, apparently put in place to make sure you do not back up your NDMP indexes to an NDMP device. This makes sense, as the scanner utility cannot be used on NDMP volumes to retrieve indexes as it does on native Networker volumes, leaving you with a Catch-22 in the event of a site recovery. The fact that they assume that NDMP index volumes shall always have “index” in their names, and no other volumes ever will is just false logic.

In the end we renamed the volumes with the more grammatically correct “indices” and called it a day.