Slow RA 90 disks on DECsystem 5XXX

[Andreas Karrer]

We have 6 DEC RA 90 disks, three on a DECsystem 5840 (BI bus, KDB50 controller)
and 3 on a DECsystem 5400 (Q-Bus, KDA50 controller).

We are not impressed by their performance. Some comparisons:

  Copy a 10 M file between two partitions on different disks
  (load average was 0.1 and less in all cases

  machine          disks                  real     sys
  Convex C 220     NEC D2363 VME           2.5     2.1 sec
  Sun 4/490        Sabre 1150 IPI          4.9     2.9
  Convex C 120     NEC D2363 Multibus      8.2     4.4
* DECsystem 5840   DEC RA 90 KDB ctrlr    29.0    13.4
  Sun 3/280        CDC Eagle SMD          33.4    12.9
* DECsystem 5400   DEC RA 90 KDA ctrlr    37.3    10.5
* DEC VAX 11/785   DEC RA 81              41.4    25.1

  (Comparison with Convex is probably not fair, these cost a bit more)

In short, disk i/o on DEC machines has hardly improved in the last 5 years.
(comparison with Convex is not really fair, these cost a bit more).
The RA90 are supposed to have a peak transfer rate of 2.8 Mb/sec...
And, these RA90 are NOT CHEAP...

 questions:
- Am I doing something wrong here? Yeah I tried upping the bufcache to 25 %,
  didn't help any. Please no benchmark flames...
- does a HSC help?
- are there third party disks (faster, cheaper, or both) for the DS 5xxx?

+-----------
  Andi Karrer, Communication Systems, ETH Zuerich, Switzerland
  karrer at ks.id.ethz.ch