• Subject: Re: Save/restore Compression algorithms....
  • From: pytel@xxxxxxxxxx
  • Date: Thu, 18 May 2000 11:26:49 -0500

Save/restore can use two different compression techniques:
- data compression - can be done in software and some older tape
drives/IOPs do it in hardware
- data compaction - purely hardware and is used by newer tape drives/IOPs

Data compaction is more sophisticated, it compresses much better and takes
less time, because it's done in a specialized hardware (outboard).
When you say DTACPR(*YES), you force system to use more primitive data
compression.
To reach best compression and performance, use defaults DTACPR(*DEV)
COMPACT(*DEV) - then system will use the best compression technique
available.

    Alexei Pytel





Greetings,

We're working on doing some system saves under program/CL control.  One of
the interesting things we found was that a save *nonsys under CL control
specifying DTACPR(*YES) took more time and more tape vs the straight GO
SAVE/21.

Is there a difference in the algorithm being used by software vs hardware?

I can see a definate time/performance difference between the 2, and I'm
curious as to if the newer hardware compression (for a 6385 tape drive in
this case) is different.

Thanks..

Don in DC

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