Path: utzoo!utgpu!watmath!watcgl!idallen
From: idallen@watcgl.waterloo.edu
Newsgroups: comp.sys.dec
Subject: choosing between ra70 and ra90 disks under Ultrix 3.x
Message-ID: <12002@watcgl.waterloo.edu>
Date: 20 Oct 89 05:47:14 GMT
Sender: idallen@watcgl.waterloo.edu
Reply-To: idallen@watcgl.waterloo.edu
Distribution: comp
Lines: 25

From: "Ian! D. Allen [CGL]" <idallen>

I'm trying to specify a DS5810 system with about 3.6 Gb of disk.

I see that the VAXBI KDB50 controller advertises a sustained throughput
of only 1.2 Mbyte/s.  This is slower than the published transfer rate
from an RA70 (1.4Mb/s) or an RA90 (2.8Mb/s).  Does this mean

    - that even with only one disk on a KDB50 controller, we won't see
      the full performance of an RA70 or RA90 disk?

    - that putting more than one disk on a controller is silly if we
      anticipate much disk use, since even with only one disk the
      controller can't keep up?

If one buys a bunch of RA70 disks (SA70 modules), does the availability
of many seek arms make up for the fact that the RA70 disks are a bit
slower in both seek and transfer rate than the RA90 disks?  Will the
slowness of the controller hide the speed advantage of the RA90's, making
the RA70's multiple seek arms a much better idea?

Should I be considering an "HSC40 Intelligent I/O Server" if I really
want to get the most out of my disks?  What do the figures mentioned
in regard to the throughput of this thing mean relative to KDB50
throughput, and can Ultrix 3.x really handle one of these effectively?