Dipto,
considering you only have it on a PII 400, you will never get anything close to the 900MB/min claimed.
What goes to making the tape drive fast..
1st, I would say the 900Mb/min is the compressed rate a 2:1, for starters, unless you are backing up alot of text files, excel, word, ie. highly compressible files, you will never ever get to 900Mb/min.
2nd, a fast processor, one is enough.
3rd, fast disk drives, at least 10k RPM, 15k RPM are better.
Thats only for starters - I think the rating done is actually the top speed of the drive, but not with any backup software.
Hope this helps
---cheers
shirmal