On 10/04/2020 11:30 PM, Chuck Guzis via cctalk wrote:
The problem arose if the program either failed to keep up
(e.g. competing programs demanding the CPU) or if an ECS
transfer occurred. Where I got involved was with a 4-CPU
configuration sharing 4MW of ECS, using the ECS for swap
space. ECS transfers completely swamp the read/write
pyramid, so the PP gets locked out and can't service the
drive. Recovery was doing a backward-read to the BOT or
preceding IRG. Lather, rinse, repeat. It was fun to watch
and we never solved that one to anyone's satisfaction.
I can't imagine any way to fix this except to put a buffer
memory in the PP big enough to hold a few records of tape
data. Probably played hob with disk transfers, too, except
that wasn't as visible.
Jon
