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160GB DAT only has 80GB capacity

Using Symatec Backup Exec 11d.  New 160GB backup drive is only providing a capacity of 80GB - I gather this has something to do with compression but I'm uncertain how to get the stated 160GB capacity.  Any assistance appreciated.  Thanks.
2 Solutions
Adam BrownSr Solutions ArchitectCommented:
A lot of tape manufacturers advertise their capacity in maximums based on a 100% compression rate. Most 160GB DAT cartridges are actually 80/160, which means 80GB uncompressed, 160GB with 100% compression. So you're probably stuck with 80 unless you turn on compression for your backups.
Fred MarshallPrincipalCommented:
The important thing is the compression ratio.  No tape manufacturer can tell you what it will be because it's not only dependent on the compression method chosen AND your actual data.  Some data is highly compressible and some is not.  So if a tape will hold 80GB and if there is allusion to 160GB, that must refer to an average compression ratio of 2:1 ... or a data size ratio of 1:2 depending on how you like to say it.

You can take a program like 7Zip which has pretty good compression algorithms available and compress some of your files just to see what happens.
t38Author Commented:
That clarifies things, thanks to you both for your input
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