[Simh] EXT :Re: PDP-10 simulation: DEUNA support help needed

[Cory Smelosky]

On Thu, 30 Apr 2015, Timothe Litt wrote:

> In DEC, volume shadowing was first built into the HSC50 (a CI-based
> disk/tape controller), released in the early 80s.  Drives were the 14"
> RA81 and follow-ons.  The early design work was in the late 70s.  The
> TOPS20 announcement of the CI, CFS and clusters predated the VMS
> announcement, to the great annoyance of the VMS crew, which had it
> running internally but wasn't permitted to announce it.  TOPS20 didn't
> support volume shadowing.  Neither did TOPS10, though it did support CI
> disks and tapes (but not clusters) later.  The CI/MSCP protocol layers
> used common code in both OSs, similar to what was done with DECnet.
> Host-based volume shadowing came considerably later.
>

So...were MSCP drives connected to the KL/KS over CI to an HSC50?  I saw 
MSCP drivers but couldn't figure out how they were attached. ;)

> I implemented V1 of the VAX Striping Driver, c.a. 1988, as a midnight
> engineering project.  It was originally proposed by the LCG I/O group as
> part of the VAX9000 development to address high-bandwidth I/O
> requirements of the HPTC market.  It turned out to be extremely popular
> for general timesharing, as it increased the sustainable request rate -
> much of a timesharing workload consists of small I/Os - to mail files,
> editor journals, and the like.  It was sold across the product line,
> more for request rate than for bandwidth.

Interesting!

Have a paper on it?  I'm interested in read/versus write speeds/latencies.

>
> However, the Striping driver was perfectly happy to stripe any
> underlying physical devices (though one wanted the sizes to be the
> same.)  This means it wasn't limited to RAID 0.  People striped
> shadowsets (host and controller-based),  which some call RAID 1+0.
> People also striped MSCP-served disks, whatever the underlying
> technology.  And MSCP-served stripesets.  Some of these configurations
> had, er, interesting performance characteristics.  But the Striping
> driver was inexpensive, and the placebo effect overcame engineering reality.
>

Unusual perferformance characteristics always make for interesting papers!

> When it became evident that Striping was a popular product, there was a
> proposal for host-based RAID.  I had nothing to do with that, having
> turned the Striping driver over to the Storage group by then...
>

Ahh.

>
>> - Mark
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>
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-- 
Cory Smelosky
http://gewt.net Personal stuff
http://gimme-sympathy.org Projects