[COFF] Disk Technology was [Simh] Which PDP-11 to choose

From: clemc at ccc.com (Clem Cole)
Subject: [COFF] Disk Technology was [Simh] Which PDP-11 to choose
Date: Tue, 2 Jul 2019 09:13:22 -0400	[thread overview]
Message-ID: <CAC20D2P=XxhGQpNy0tb-5=dWz-R16Dkb1+=9figy1onRMNHqHw@mail.gmail.com> (raw)
In-Reply-To: <CAC0cEp87V3OsNJteCHzQXD0x7hDerwmDrTqJ+P9jhXXjORjXYw@mail.gmail.com>

Yeah - although we discovered that the better the controller microcode was
at handling errors, the better life was for the user, disk vendor, and
system manufacturer.   On the VAX, the SI controller was not extremely
forgiving and I had left that world. I wonder if some of the super eagle's
issues were that the controller did not gracefully handle drive errors.
IIRC Emulex's SMI and Unibus controllers tended to be smarter than SI's.
 FWIW: Once Xylogic did the 45x series for the Multibus/later VME with *the
microcode solid* and Unix drivers got written to handle the errors
returned, my experiences were ( as Larry said ) we had few problems with
any of the SMD disks, even the Ampex, at either Masscomp or Stellar.

Truth is by then we had started to concentrate on ESDI 5.25" FF disks from
the 19" and 8" SMD technologies (using a cheap SCSI to ESDI controller).
But it was a little of "you get what you pay for" problem.   The new
controllers for the smaller disks cost a lot less  (Xylogic VME/Multibus
*vs.* SMS SCSI); so we were starting over with the SMS folks to educate
them.  Apollo had been SMS's primary partner (did you ever wonder why they
supported at 1056 byte block as one of their native block sizes), but to
the SMS's folks credit they picked up the ideas of good error recovery
reasonable fast.

Clem

PS The thing I fear lost to history was PC's code for the Masscomp
formatter/tester/exerciser for the 45x Series. It was an amazing piece of
work.  I think we still have the OS sources kicking around, but the
diagnostic system was of less interest I fear.

On Tue, Jul 2, 2019 at 7:47 AM John P. Linderman <jpl.jpl at gmail.com> wrote:

> There were eagles, and then there were super-eagles. Our experience with
> eagles was great, and we were eager to try the (larger) super-eagles. We
> soaked them for a month or so, then put them into production use.
> Whereupon, they started dropping like flies. It turns out the glue they
> used to attach the platters to the spindle slowly crept out over time,
> eventually coming to grief with a read/write head. This experience was
> wide-spread, and seriously damaged Fujitsu's reputation.
>
> On Mon, Jul 1, 2019 at 10:11 AM Larry McVoy <lm at mcvoy.com> wrote:
>
>> On Mon, Jul 01, 2019 at 09:49:42AM -0400, Clem Cole wrote:
>> >  An Eagle or Eagle-II was a whole lot lighter (and physically smaller)
>> than
>> > an RP06 or RP07 (or an RM series drive for that matter). It is
>> interesting
>> > to hear you had problems with the Eagles.   They were generally
>> considered
>> > the best/most reliable of the day.   The SI controller on the Vax was
>> less
>> > so, although many of us in the UNIX community used them.
>>
>> We ran Eagles on the Masscomps we had at Geophysics.  Nothing but good
>> things to say about those drives.
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>
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