ganiuszka wrote:

> mt-gnu can not switch the hardware compression but mt-st can switch it.
> 
> In addition, in mtx tools you will find program called tapeinfo. It can 
> show the hardware compression state for a tape drive and much more.

smartctl will also provide useful information if the tape drive supports it.

Please note a few of things about hardware compression (these really 
should be in the FAQs)

1: Almost all tape devices default to hardware compression ON

2: It's almost always faster than software compression

3: Although usually not as effective as software compression, the 
difference normally runs to less than 5% and the time/cpu overhead of 
running software compression is expensive.

(You'll gain about 5-7% with software compression at maximum settings 
over hardware compression.  It's not enough to be bothered about. 
Honestly, tapes are cheap and the throughput penalties will wipe out any 
savings)

4: Software compression typically slows data throughput to an absolute 
maximum of 30MB/s (even on localhost or across a 10GigE network)

5: In all modern(*) implementations, if what comes out of the hardware 
compression engine is larger than what went into it, the drive will 
write uncompressed data to the tape (eg, when backing up 
already-compressed files)

(*) Where modern is "everything less than 20 years old"


Software compression has its place, but that place is slow WANs or on 
disk partitions. NOT on LANs of any flavour or on tape.




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