I would likely go for MSDP pool. While advanced disk give you the same capacity as the file system, a MSDP disk pool can give you many times the capacity because backup images are being stored are deduplicated and compressed.
If backup data is encrypted, MSDP will not help you in gaining more than physical capacity.
There are some preparation to do before deploying a MSDP pool , please see :
Please be aware that Netbackup 7.7.3 has end of technical support May 5, 2019
Are you duplicating the data ?
If not, I personally wouldn't write it to disk at all, I'd goto tape ...
Why, a single copy of data is safer on tape than disk - yes tapes can and do fail, but you lose only that one tape, disk failues can be 100% data loss - everything ... RAID offers some protection, but not complete.
Ideally, both - write to disk, duplicate to tape for longer term storage.