In terms of reliability and maintenance effort we believe hard-disks are superior to tapes.

If properly cared for, tested and verified tape backup can be reliable, however this involves extra work. Additionally tapes should be verified on a different tape-drive to the one which took the backup. Over time head alignment issues can mean the tape is only readable on the tape-drive which took the backup, if you lose that drive the tape is useless.

Hard-disks in a RAID configuration mean a hard-disk can fail and the backup is still available. There is no verification, cleaning or other maintenance required.