Quote:
it's electrically possible and protocol-possible, but, I think, only as a side effect of the specfication, not as a design point.

Multi-master was one of the original concepts in SCSI 1 following on from the original SASI single master spec. The concept was properly codified in the SCSI 2 spec. I operated a multi-master setup in a medical imager, but the targets were not block (ie. disk) device classes (at least not with modifiable device attributes).

A lot of the access control mechanisms are actually built into SCSI at the protocol level (ie. devices and in the transport) but due to the massively Windows-centric nature of the user world since the mid-90s, master-to-disk type single controller setups have become prevalent, and about 90% of the SCSI spec remains unused, with many devices not using a significant proportion of the available capabilities of the bus. Our system talked to a CPU, Co-processor and an ultrasound Scanner (as a block class device) in parallel between two host controllers. A really impressive, rapid system able to do a lot of parallelisation - just by exploiting more of SCSI's feature set.

Shame. SCSI had enormous potential. Never exploited, and under-used: now it's been committed to the graveyard.