compressed backup

[Franklin Bockstael]

My DLT VS80 can backup 40 GB or 80 GB compressed.
How do I tell the VS80 wich size to use.
I am using Windows 2000 Server backup 5.0.

[Lewis Finch]

Actually the tape drive has hardware compression enabled by default so you don't really "tell it" to do anything. D0 not use software compression just let the drive do it's job

[Franklin Bockstael]

i don't think thats the case, please have a look at the attachment.
I tried to write about 55 GB but the drive stopped at 36 GB giving me the error the tape was full and another one had to be loaded to continue writing.

[Lewis Finch]

If the data you are backing up is already compressed you cannot compress it more. I suspect that is what's happening

[Franklin Bockstael]

Unfortunately it were just mp3 files, not compressed data.
But do I understand this right?
If I try to copy files that are already compressed I can backup no more than 40 GB. If the data is not compressed it has to be data that can be compressed more than 2 times to fit on the tape. Then 80 GB data becomes 40 GB and that is written to tape.
So the tape never contains more then 40 GB data?

[Lewis Finch]

loosely interpreted you are correct. Here is a link to help explain compression. MP3's are compressed by the way. 2-1 compression is an undustry standard but your tape also has to contain header information (table of contents) as well as compression algorythm that is being used so you do lose some space to "overhead". I would say in your situation you are doing just fine with what you are getting on your tape.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50460