Long backup time.

I agree with Quindor - to 'backup' the backups from disk to tape, you need to 'Duplicate' the disk images.

It can be done automatically using Storage Life Cycle Policies.

The data on disk is Dedupe data? You need to understand that duplicating this data to tape will need to 'rehydrate' the backup images, i.e. all data needs to be written to tape and not just the unique segments that was written by the backup image to be duplicated. Performance therefore can be expected to be on the slow side...

See chapter 14 of Administrator's Guide for Windows I  http://www.symantec.com/docs/TECH127079 for detailed info on SLP's.

PLEASE also read the Performance Tuning Guide - it covers SIZE_DATA_BUFFERS_DISK and other 'BUFFER' files that are used for tape...