Hi,
USB tape drives are currently not supported with Backup Exec 9.1.
If they are supported in the future, the Hardware Compatibility List will get updated as well.
The HCL:
Symantec Backup Exec for Windows Servers (tm) 9.x (9.0, 9.1) Hardware Compatibility List. Includes HCL information for supported drives, libraries, virtual tape devices, fibre-channel HBAs, switches, routers/bridges, and iSCSI components. For printing purposes, the latest version of Acrobat is recommended.
http://support.veritas.com/docs/282347
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