Disk I/O speed dropped dramatically after adding 2nd SCSI controller....

From: Thomas Leitner <tom_at_finwds01.tu-graz.ac.at>
Date: Wed, 18 Dec 1996 13:06:02 +0100 (MET)

Hi,

As suggested in this list, I bought one of these $50 NCR PCI SCSI
controllers and plugged it into my ALPHAPC64 board running Digital
Unix 4.0A. Everything went fine. The controller is seen in the
console and so are the devices attached to the controller. After
rebuilding the kernel with "doconfig" which just added the lines:

 bus psiop1 at pci0 slot 6 vector psiopintr
 controller scsi1 at psiop1 slot 0

to the config file and changing /etc/fdmns/inw_dmn to contain links
to the new devices /dev/rz8c and /dev/rz9c everything is up and
running as it was before.

Now out of couriosity, I've ran the BONNIE disk i/o benchmark to
see if anything has changed in the I/O speed and I found the following
dramatic differences:

before adding new controller

              -------Sequential Output-------- ---Sequential Input----Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block-----Seeks---
Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
          100 3700 73.9 6321 27.5 1588 7.5 4947 87.5 7850 22.9 135.1 4.8


after adding adding 2nd SCSI controller

              -------Sequential Output-------- ---Sequential Input----Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block-----Seeks---
Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
          100 2187 45.9 2514 12.9 982 4.8 2192 39.3 2510 8.0 109.6 3.5

and this is on both, the old SCSI controller with only the system disk
attached, as well as on the new, 2nd SCSI controller with the users home
disks attached.

Needless to say that this is not quite satisfactory.

Questions:

1.) I left the default INTA# interrupt configuration on the new
    controller? Should I change to INTB# ? Would this help?

2.) In console mode, I've entered "isacfg -init" and "init". Is it
    possible that this re-sets some SCSI variables to the default?

3.) Is it possible that both controllers somehow now are defaulting to
    non FAST SCSI or something? (I remember the FAST_SCSI_A and
    FAST_SCSI_B settings on the old DEC 3000/600) ?

4.) Any other ideas anyone?

Thanks a lot -- Tom

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Received on Wed Dec 18 1996 - 13:27:41 NZDT

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