Not getting very good performance on the 3590


  AIX 4.1.4
  RISC R24
  Tape 3590-B11


  Customer has just installed his 3590-B11 Tape drive and through testing
  has determined that he is getting only 2mb/sec throughput.

  I first had the customer upgrade the device driver to Atape.driver

  To determine the throughput of the tape drive only, leaving the hard
  disk out of the picture run this command:
  This command builds the data in memory first then writes it to tape thus
  taking the hard disk out of the picture.

  time tapeutil -f /dev/rmt0.1 wtest -b 262144 -c 1 -r 500
  131072000 bytes written

  Real Time = 13.84 seconds

 The tape drive is running at expected rates.

  Next I had the customer use his normal backup command, tar in this case
  and backup to /dev/null.  This provided a throughput of 4mb/sec.

  Customer should expect to push the 4mb/sec number but will not achieve 9mb/sec
  due to the bottleneck of the disk drives.

 Customer was receiving only 1-2m earlier.  I explained that the new
 driver help that.  I also had customer set block size of the tape
 drive to 256k (262144) which is the optimal block size for the 3590.

NOTE:  Make sure the buffer size of the backup command 
       being run is a multiple of the block size.

       Example:  If the block size of the tape drive is 262144, 
                 then the command being run needs to be 

               tar -b512 -cvf /dev/rmt0 /filesystem

               tar -b512 -xvf /dev/rmt0

Support Line: Not getting very good performance on the 3590 ITEM: BN4947L
Dated: September 1996 Category: N/A
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