Dat tape capacities
 

I have just bought a HP dds4 tape drive.

I am trying to backup some video files, but the tapes keep reporting there full too early ?

i can only get 10gb out of DDs3 supposed to be 12gb native 24gb compressed.
DDs4 i can only get 16gb onto a tape supposed to be 20gb uncompressed 40gb compressed?


does any one know why this is happening ? I have used dat drives at work and can easily get 80gb sql databases onto dds4's. and have never got under their native capacities

I have checked that Hardware compression is enabled, has anyone else had this ?

hmm just done a backup and the driver shows that tape compression is disabled. it was enabled before i did the backup ?

I am using windows XP backup which is set to compress data

'Compressed' capacities are just marketing figures - ignore them. The compression ratio you get depends on your software and the nature of the data being compressed; video files are already highly compressed and certainly won't compress any more. So, it's the native capacity you're interested in.

It could be that you and the tape manufacturer have different opinions as to what a gigabyte is - for marketing reasons again, funnily enough. A gigabyte is 2^30 = 1,073,741,824 bytes, but storage media is often sold in units of 1,000,000,000 bytes.

So, your 10 'real' GB of movies require 10.7 'marketing' GB of storage.

Does that explain it?

tis the same with hard drives. suppliers always quote "unformatted" capacities. my 2 x 160 SATA drives when formatted are only 152gig. :(