Disk storage units supported with Exchange Granular Recovery Technology (GRT)
Granular backups must be made to a supported disk device. During the backup operation, the mailbox name or top public folder is cataloged. When you duplicate (-bc_only) a backup, NetBackup catalogs the entire contents of the backup image and the duplication can be targeted to any media. When you perform a restore, the primary backup image must exist on a supported disk media. You may need to perform another duplicate operation to copy the backup to disk.
More information is available on the disk storage units that are supported with GRT.