Solaris

How can I tell (from the command line) is compression is turned on for a tape drive?

I need to backup a system that is approx 150gb to a tape that has 110gb uncompress but 220gb available compressed.

Any ideas?
Also is it possible to turn compression on or off from the command line?

I am using Solaris 9

Most tape device drivers in UNIX support compression at the hardware level assuming the physical tape drive supports it. Compression is enabled or disabled by specifying the appropriate tape device. Tape density can also be specified in this manner. Refer to the st(7D) man pages for a detailed list of driver options.

For example:

tar cvf /dev/rmt/0hc directory-name # high density, hardware compression

or

tar cvf /dev/rmt/0h directory-name # high-density, no compression

Remember, hardware compression rarely increases overall capacity if the data stream is already compressed. That is, if all the files in the above example "directory-name" are already compressed, enabling hardware compression won't "double compress" and could easily increase the tape required due to duplicate overhead of the software and hardware compression algorithms.