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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