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Determining I/O Performance Bottlenecks?

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The Question is:

I' ve got a TL891 under VMS 7.2-1 with a performance up to 2GB/Hr.
I read the manuals and it say that the performance must be 30GB/Hr.
Here is the command which I use to backup with tapes type III and IV.
$ init/media_format=compaction $10$MKA400: 000788
$ Mount/media_format=compaction/Fore $10$MKA400:
$ Backup/Density=TK87/media_format=compaction-
   /label=000788/verify/ignore=interlock/log -
   backup_area:*.*;* $10$MKA400:barea.bck/save_set
Is something wrong??
Why I have this bad performnace??
Thaks, Diego Cabezota Artola

The Answer is :

  Most (all?) bandwidth values cited are either the peak performance
  or the peak sustained performance, actual transfer rates can be lower
  due to other performance-limiting factors, including the system bus
  speed, the SCSI bus speed, the source disk speed, the available
  system performance, the process quota settings, the level of
  fragmentation on the input device, I/O contention, and a plethora
  of other potentially contributing factors.
  As you have not included details on the SCSI bus configuration,
  the source device, the process quotas, the available system
  resources, etc., no specific answer is possible.
  For a procedure to review performance, please see the performance
  manual.  For the recommended process quotas, please see the System
  Manager's manual chapter on BACKUP.  For system tuning, please see
  the AUTOGEN mechanism (and FEEDBACK) and associated documentation.
  If your input disk is fragmented, defragment it.
  If your system configuration simply lacks the required I/O bandwidth
  (eg: a SCSI-1 bus is limited to roughly 4 to 5 megabytes per second
  aggregate, and a PCI-33 bus cannot exceed roughly 132 megabytes per
  second aggregate), you will need to upgrade the I/O bandwidth and/or
  the system configuration.

answer written or last revised on ( 14-MAR-2001 )

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