Explain Compression PLEASE!

[Nick Sharpley]

Can someone explain to me how the tapes compression works?
They are 400Gb tapes (assuming 2:1 compression) but in Veritas Backup Exec I cannot get more than about 268Gb onto a tape.

How can I get the compression that the HP tapes claim to offer????

Many thanks.

[Uwe Zessin]

You have correctly written: "assuming 2:1 compression".

This is only an assumption and HP does not claim their tape drives can do a fixed compression reatio, because it depends on the backup data.

Some data (an empty database whose files haven been zero-ed) will compress greatly, but a disk full of .ZIP files might not work at all, because they are already compressed.