Slow RA 90 disks on DECsystem 5XXX

[Greg Pavlov]

In article <1990Dec12.194341.18284 at bernina.ethz.ch>, karrer at bernina.ethz.ch (Andreas Karrer) writes:
> 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

> * DECsystem 5840   DEC RA 90 KDB ctrlr    29.0    13.4
> 
  The best output that I have seen from a KDB controller, driving an RA90 on
  a 5810, is apx. 100 "logical" i/os/sec, or apx. 800KB/sec, if logical block
  size is set to 8192 bytes.  So the time you report, disk-to-disk on the same
  controller, is in sync with that  (since the controller is reading from one
  drive and writing to another). 

  If you execute iostat in the background while trying different combinations
  of reads,  e.g., cp file-on-disk1 /dev/null, followed by the same, but put-
  ting it in background and simultaneously cp file-on-disk2 /dev/null, then
  do the same with 3 reads from three disks, you will see that the kdb will
  tend to pump the same TOTAL amount of data, irrespective of number of disks
  being accessed.  E.g., behavior on a par with a cheap and unsophisticated
  SCSI interface....
  
> - does a HSC help?

  Probably.  But, depending on your needs and budget, a second KDB may be
  enough.  At $10K list you are paying monopolist's prices, but that's still
  a fraction of the cost of an HSC.....

> - are there third party disks (faster, cheaper, or both) for the DS 5xxx?

  For the 5400 definitely yes, since the QBUS was invaded a long time ago. 
  Someone else may have some up-to-date info re the BI bus in the 58nn.

  Note that you don't necessarily need to find something faster.  Example:
  SCSI interfaces for the QBUS can be purchased for less than $2K, compared
  to the $6K for the KDA (minus discount, of course).  So if the SCSI is 
  "only" as fast as the KDA, you can buy at least two for the same price and
  accrue additional overall performance to boot.

   greg pavlov, fstrf, amherst, ny

   pavlov at stewart.fstrf.org