On Wednesday, March 8, 2017 at 11:50 PM, Johnny Billquist wrote: > On 2017-03-09 02:26, Paul Koning wrote: > > > >> On Mar 8, 2017, at 7:44 PM, Johnny Billquist <b...@softjar.se> wrote: > >> > >> On 2017-03-08 22:15, Bob Supnik wrote: > >>> The HSC family offered a superset of capabilities compared to the > >>> UDA50/QDA50. In particular, > >>> > >>> - tape as well as disk support (TMSCP as well as MSCP); > >>> - controller-based disk to tape backups and tape to disk restores; > >>> - controller-based disk to disk duplication; > >>> - controller-based volume shadowing (RAID 1). > >>> > >>> UDA50/QDA50 did not support tape drives, disk duplication, or > >>> controller-based volume shadowing. > >>> > >>> HSC supported some data caching; UDA50/QDA50 did not. > >> > >> Oh. I didnät mean to imply that the HSC was just the same as an UDA. But > >> the MSCP protocol as such is the same between them. Shadowing, local disk > >> copying, caching and so on, are just things a controller can do without the > >> host are even aware of it happening. > >> But since we're talking emulation, the actual disks now might be doing > >> even more of that than an HSC ever could. It's not really something that > >> makes much sense to emulate. > > > > I think the significant different for emulation, as opposed for the real > > hardware, is that CI is a multi-access network (like Ethernet). All the > > hosts can > > see all the disks, and in addition the hosts have peer to peer > > communication. > > VAXclusters use both of these things. You can of course do them via LAVC > > (same services but over Ethernet). With CI emulation you get a second way. > > That enables running clusters with VMS versions predating LAVC, if that is > > interesting to anyone. > > Yes. > > However, to get that working you will either need to run several emulated > machines under the same simh instance, or have the CI run outside of the > simh framework, so that several simh instances can communicate with it. > While possible, this could turn complicated. > If you only do CI within CI, with the limit to one machine, then all that is > lost, > and you end up with the same as a local MSCP and TMSCP controller, with > just a different transport layer you need to implement.
When Matt Burke initially was working on this, I believe that we talked briefly about extending sim_ether to support packet delivery across IP multicast. With that model, all of the systems connected to a particular star coupler would use the same multi-cast group. I think that DEC may have done something very similar to this when they implemented LAVC. Several independent Local Area VAX Clusters can certainly coexist on the same LAN without interference. - Mark _______________________________________________ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh