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Tuning BACKUP Performance? Block Size?

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The Question is:

 
What is the optimal block_size setting when
performing an image backup to a DLT IV tape
drive?

The Answer is :

 
  Usually a multiple of 4096 blocks for DLT, 61440 being a typical choice.
 
  If you trust the SCSI bus and the DLT hardware and particularly the DLT
  CRC processing, /GROUPS=0 and /NOCRC can be reasonable -- this choice
  is usually based on the perceived value of the data, and the history
  with the hardware.  (BACKUP with the XOR grouping and CRC enabled will
  provide end-to-end verification of the data.)
 
  Enabling compaction can help with tape usage and with the reduction of
  the physical media access bandwidth -- this compression usually (but not
  always) decreases the amount of data that is written to the DLT media.
 
  Also configure the BACKUP operator username account per the process quota
  settings referenced in the OpenVMS SYstem Manager's manual.
 

  
     
     answer written or last revised on ( 15-NOV-2002 )
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