I recently acquired a MicroVAX 3100/90, my second VAX system. Since I now have two VAXen, I thought it might be interesting to try setting up a little two-machine VMS cluster, particularly since both of my systems complement the shortcomings of each other (the 3100/90 is about twice as fast as the 4000/60 by the benchmarks I've seen, while the 4000/60 has a video card and a bigger, faster hard drive.) But I don't actually know that much about VMS clusters aside from that they exist. I'm currently looking through some of the documentation, but I figure it can't hurt to ask some of the basic questions I have:
* I know that a VMS cluster consists of separate instances of the operating system running on separate machines. To what extent can they share a workload, aside from sharing disk storage? Can VMS, say, assign processes launched from one machine to run on another? Can it do so automatically based on some criteria (for example, launching compiles on the faster machine,) or does it have to be specified?
* I know X Windows was designed for this from the start, so I assume it should be possible to run DECWindows programs on the 3100/90 and have them display on the 4000/60?
* On a tangentially-related note, is it possible to set up any kind of RAID-style disk striping/mirroring? The 3100/90 has four rather pokey 406MB hard drives, and I don't have the play budget to replace them with something newer, but striping data two or four ways across them should get the throughput up a bit.
Edited by commodorejohn on November 30 2014 16:00
Plenty good enough for my purposes (though I'd like to see the system that can move running processes across machines!) Mainly it would just be useful to be have intensive stuff like Mosaic or VAX C run on the 3100, since it's so much faster.
RAID/Striping would be hardware dependent. You can shadow/mirror using VMS Shadow sets.
So it looks from the overview like shadowing provides redundancy, but doesn't really improve read performance? I suppose that could be useful (the drives in the 3100 are kind of old, so redundancy for the boot volume could be nice, and I don't plan on doing a lot of access to them since I've got a newer, zippier drive in the 4000.)
(Speaking of sharing storage access, I see that I can set up a multiple-host SCSI connection for this purpose - I'm assuming that the drives in both systems have to have unique SCSI IDs? What about the host controllers? Can that be set from the firmware prompt?)
Edited by commodorejohn on December 01 2014 07:25
You need specific hard to set up a DSSI shared SCSI cluster. I believe you will be limited to a network cluster with your present hardware. You could easily build and cluster in a Simh virtual VAX for faster and larger storage.
Shadowing helps performance in that in provides multiple spindles to read/write data.
As far as I know, there are no supported multiple host SCSI configurations for VAX.
Shadowing may speed up reading as the first read to actually complete completes the I/O. Shadowing slows down writes as both writes must complete to complete the I/O.
I have not yet tested this, but have considered setting up a SimH/VAX system to be dedicated as a cluster node only to LAVC serve disks to VMS clusters. For the older VAXen, the 10 Mb 1/2 duplex speed would be the main limitation.
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