11/70 <-> uVax II link

[P. D. Guthrie]

In article <440 at rna.UUCP> dan at rna.UUCP (Dan Ts'o) writes:
>In article <1486 at uwmacc.UUCP> jwp at uwmacc.UUCP (Jeffrey W Percival) writes:
>>We have a PDP 11/70 running 2.8BSD.  We are thinking of getting
>>a MicroVax II, and getting Berkeley Vax Unix to run on that.  Instead
>>of trying to get networking going on our 11/70, we thought we'd
>>get a Systems Industries disk and controller that will be shared
>>by the two machines.  Is this a reasonable approach?  Our
>>expectation is that file systems on the shared disk will be
>>accessible to users of both Unixes.  Are the 2.8/4.2 file systems
>>identical?  Can we just "mount" a shared file system on each of
>>the systems, so that the directories and files in that file
>>system appear in the directory paths of users on both machines?
>
>
>	- You are also screwed because even if they were two identical machines
>or filesystems, you could not mount them both read-write (and get away with it).
>As soon as one UNIX wrote the filesystem, modifying inodes and the freelist, the
>other would get mighty confused. Indeed, even mounting only one read-write is
>not a good idea, though probably not fatal. You could devise some kind of
>locking scheme to allow multiple read-write access. A lot of work. Just
>having both read only would be okay.
>
>	- Since the MicrovaxII is a Qbus machine, you will need a Qbus
>controller from System Industries that is format compatible with and can dual
>access with your Unibus SI controller. Most Qbus SMD controllers do heavy
>interleaving (3:1), more so than Unibus controllers, thus making the two
>not format compatible. Perhaps SI does, I don't know.
>

If I remember correctly from some junk mail from SI, they offer a system
for two Micro-vaxes to share the same disk drive. They must provide some
sort of device driver mods for both Ultrix and Vmess, I would expect, so
the above may be possible. What I would be interested in is if it would
be possible to format one partition VMS, and one Unix, and run each OS
on one machine. You then write a device driver for each OS to access the
partition and format of the other machine, allowing for quick and easy 
Unix <=> Vmess conversion, and of course, the advantages of both OS's
for your data. Any opinions?

					Paul Guthrie.