jdc@rama.UUCP (James D. Cronin) (05/17/88)
I recently asked about third party disk expansion for MicroVax II's. I
would like to thank the people who replied. Pim LIttle, jpl@edison.GE.COM
asked for a summary of the responses. Here they are, more or less
intact:
From Bill Wyatt, {husc6,ihnp4,cmcl2,mit-eddie}!harvard!cfa!wyatt
> We are considering expanding our MicroVax II's by adding third
> party disks/controllers. We are considering a Q-bus SCSI
> interface with a 150-300 meg disk. I would like to mount the disk(s)
> in a separate cabinet with its own power supply (we have "small-box"
> MicroVaxes). I have a few questions, though.
>
> Would we be better off with a EDSI or SMD interface instead of SCSI?
> Do they offer the same ease of expansion (i.e. daisy-chaining)? Is
> one significantly faster then the other?
I think there's little difference currently, although SCSI can go
faster. Right now, I think there are more disks & controllers doing
ESDI, though that may be changing.
> Most of the controllers claim to emulate DEC's MSCP. How close are
> they to the "real thing"? Does MSCP emulation mean you can boot
> off that disk?
The ones I'm familiar with (Emulex QD21/Maxtor 4380 = ESDI,
Aviv Corp. DFC904/Maxtor 4380 & 8760, also ESDI) seem to do
excellent MSCP emulation. And yes, you can boot from them. We do, on
some systems.
> It just seems to easy, and the prices are suspiciously low (compared
> to DEC). Are we missing some important point?
The important point you're missing (apparently) is that DEC's
peripherals are ridiculously overpriced and underperforming
compared to what you can do by going 3rd party. Usually, we buy
our systems with as few DEC peripherals as possible, and add
on 3rd party for mucho fewer $$$. Often, DEC will pick up the
maintenance, too, but usually it's cheaper to keep a spare around.
-----------
And from Steven M. Ward, harvard!cfa!ward:
I can give you lots of information on this topic. I have installed
about thirty ESDI disk drives onto BA23 VAXstations and MicroVAXes
in the last year.
The Webster/Sigma Q-bus MSCP controller is excellent. There is
an ESDI version and an SMD version. I use the ESDI version.
I use four ESDI MAXTOR or equivalent drives in an external chassis,
rack or table top. I am using 380MB drives (MAXTOR and Hitachi) and
760MB drives (MAXTOR).
You can boot from this controller/disks, but I use an RD54 in each
chassis.
I buy the chassis/power supply from Trimm and package/integrate all
items (controller, cables, chassis, drives) together. This is very
cost effective but you might not want to do your own packaging. If
not, you might want to talk to Sigma about a subsystem, though buying
packaged subsystems always cost more.
I keep a couple of drives as spares on-site and do my own drive
maintenance on these ESDI drives. Maintenance consists of sending
bad drives back to the manufacturer for a flat-fee repair. These
drives are small and robust enough to take this approach. They
also seldom fail. We save a fortune compared to the cost of maint.
per megabyte per year for our older 8/10/12/14 inch SMD disk drives
which require on-site maint. contracts due jto their fragility and
size and cost to repair on a per-instance basis.