Hello,
The IDR data has to be either on floppies or a hard disk. However you can backup the data on a USB drive.
Refer to the following technote:
Title: Backup Exec for Windows Servers support of USB or Firewire interfaced devices
http://support.veritas.com/docs/273710
Also check the chapter on IDR from the Administrator's manual for Backup Exec. Here is the link for the download:
http://support.veritas.com/docs/269777
In case of further queries, revert with details.
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Regards.