ITEM: BN4947L

Not getting very good performance on the 3590

Question:

Env:
  AIX 4.1.4
  RISC R24
  Tape 3590-B11
  Atape 2.4.4.0

Desc:

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

Action:
  I first had the customer upgrade the device driver to Atape.driver 2.5.2.2.

  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 
                 this:

               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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