There is a problem with high performance DLT operation, software compression
and system performance.



When replacing a DDS3 with a DLT7000 FWD tape drive we should see a
performance increase of at least 4 times the performance.  If everything is
configured for performance you should get roughly 7.2Gb of storage with
compression on a DDS3 drive and roughly 35Gb with hardware compression.
When software compression is thrown in the equation there are different
results depending on the performance of the system.  The reason seems to be
due to the CPU having to compress the data and pass it on to the DLT Drive.
The DLT is a streaming device and would prefer the data to continue without
stopping.  Simply the DLT is having to stop and sometimes reverse to start
again.  Using my technical term "wish/wash".  I have used the maxtapebuf 32K
option with little to no help as the DLT7000 is backing up much faster than
a lousy 16KB increase.



I have seen this occur on a number of smaller systems.  Once you get into a
multiple processor system of any kind or really anything faster than 987/988
the problem goes away.  Of course the other way is stop using the software
compression software.



Does anyone have any ideas in this regard..



Regards,



Bill Green

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