balancing scsi devices between controllers

From: Dave Carter <carter_at_mailhost.lanl.gov>
Date: Fri, 16 Feb 1996 11:02:00 -0700 (MST)

i have a question about balancing scsi devices between two
controllers.

i have a DEC Alpha 3000/300LX, which came with an internal 5 MB/s SCSI
controller to which i am adding a turbochannel KZTSA-AA 16-bit
differential 20 MB/s controller. eventually, i will be getting some
fast/wide diff scsi disks, but for now, i need to balance the devices
that i have, between the two controllers, using a differential 16-bit
to single-ended 8-bit SCSI bus converter for my narrow SCSI disks.

the 6 SCSI devices that i want to balance are:

1 1GB RZ26L (the system disk)
2 9GB Seagate ST410800N
2 9GB Micropolis (basically the same as the ST410800N)
1 Quantum DLT4700 (DLT 7-tape autoloader)

the goal is to optimize the r/w speed of the 4 9GB drives---i don't
really care about the speed of the RZ26 or the tape drive (not even
during backups).

so my question comes down to this: should i put all 4 9GB drives on
the faster KZTSA-AA, or should i put two on each controller, even
though the KZTSA is so much faster? i.e. is the KZTSA so much faster
than the on-board narrow controller that it can handle all 4 drives
better than splitting them between the controllers?

two possible configurations would be:

1)

on the on-board
single-ended controller: | on the KZTSA:
--------------------------------------------
  RZ26L | DLT drive
  2 9GB drives | 2 9GB drives
--------------------------------------------

or 2)

on the on-board
single-ended controller: | on the KZTSA:
--------------------------------------------
  RZ26L | 4 9GB drives
  DLT drive |
--------------------------------------------

also, i am not too concerned about the speed of the server while
writing to the DLT drive. all 9GB drives are AdvFS partitions, if
that makes any difference at all. i am not running LSM yet.

is there a quantitative way to predict the optimum arrangement (other
than bringing my system down to try the different combinations---not a
popular option.)

thanks for any advice.

                                - dave
Received on Fri Feb 16 1996 - 19:21:40 NZDT

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