🚀 go-pugleaf

I'm planning a purchase of a VAXstation 4000 model 90, and I'm considering
putting a 2nd SCSI adapter on its TurboChannel.  I'd like some feedback on the
wisdom and justifiabiliy of this approach.

My reasoning so far has been that I can foresee, within the next year, placing
external 4 SCSI devices externl to the system, which will already have the
internal RZ25 disk and a CD-ROM, making 7 SCSI units in use (including the
cpu), out of 8.  The additional devices would be a high-speed 1.7GB disk, a
rewritable optical drive whose media is likely be mounted /SYSTEM and accessed
by all, a 6250bpi tape drive, and an 8mm tape drive (5GB capacity) used to
import daat (weekly) and to back up the entire cluster's disks (5GB worth) on a
daily basis.

Question #1: Is a 2nd SCSI adapter the only (best? least expensive?) way of
making an additional set of units available?

Another, somewhat realted question, is about the bus load and how it may be
balanced.  Assume a moderate to heavy i/o use on this workstation: data
frequently being transferred between disk, optical, and tape, as well the
probability that this will be the boot node in a VMScluster.

Question #2: Could the SCSI bus turn into a bottleneck for even a workstation
as powerful as the VS4000 model 90 and impair its effective use?  If so, how
likely is that, and how much of an impairment do you foresee?  

Separating the devices amoung two SCSIs would only partially help, by the way,
since (and you can correct me on this, as I'm guessing) one of the SCSI's would
be internal devices only and the other would be external devices.  This would
split off the system disk traffic (CD-ROM is negligable for now) from the rest
of the i/o, but would leave big hitters on the external SCSI (big disk, two
tapes, optical).

Question #3: How much of an i/o load reduction in this type of configuration
would adding another SCSI adapter be?  Would the remaining devices on the
external SCSI still present enough of an i/o load that they would interfere
with one another and with user programs?

You can email to me directly at bleau@umdsp.umd.edu and I will summarize and
report in about a week.  Thanks.

Larry Bleau
University of Maryland
bleau@umdsp.umd.edu
301-405-6223