tape compression

[Bill Campbell]

On Wed, Feb 27, 2008, Vu Pham wrote:
>My Linux server has a tape drive SDLT320, which is supposed to be able 
>to store 320Gb data with compression.

Caveat emptor.

The numbers claimed for tape compressed capacities are generally
bogus, assuming 50% compression.  This can be very optimistic,
depending on the type of files being written.  I've never really
trusted tape drive's hardware compression, preferring to use
smart backup software which handle the compression themselves and
keep track of the tape capacity.

Programs such as BackupEdge and Lone Tar do file by file
compresssion, and don't try to compress files that are already
compressed as attempting to further compress a compressed file
may well result in a file that's larger than the original.

Bill
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