Question : Problem: Tape Backup Overruns DAT72

I back up Small Business Server to tape daily and we've reached the point where data volumes are exceeding the tape capacity.  I run our system but am not expert, and would appreciate a few pointers as to what to do. In particular
1. The tape is supposed to be 72GB (tapes are HPDAT72 C8010A), yet our data is around 37GB. So why does it fail when it should only be half fulll?
2. At the moment we backup up the whole of the C:\ drive. Is there anything we could probably safety exclude from the backup ?
3. If we were to upgrade our backup storage capacity, what are the best options ? Are there tapes with greater capacity ? what about hard drives (what about need for removal offsite ??) Online backups (is this practical for 37 Gbytes ?)    

Answer : Problem: Tape Backup Overruns DAT72

1. DAT72 drives are only 'nominally' rated at 72 GB. The guaranteed capacity is around 36Gb. The 72 assumes the data can be compressed at a ratio of 2:1. If you're only getting 37Gb (and if the media is not excessively old and the drive heads are regularly cleaned - ie, it's not because of write errors) then it suggests the data is not compressible. Are you backing up a lot of jpegs or video files?

If the current block size is something small - like 512 or 1024 bytes - you can sometimes eke out more storage on a tape by increasing the block size, but I don't recall if this works on DDS drives, which are a strange technical fudge overlaid on top of the original DAT (an audio) format.

2. Are there some files that aren't getting updated regularly? Then back these up separately, and don't back them up daily.

3. If you're on a budget and you want to maintain instantaneous backwards compatibility then move up to DAT160. Or, if you're happy to swap drives (or leave the old drive still connected in tandem with a new drive) move up to LTO2 or 3.