4.1 and vms on same disk anyone?

[z at rocksvax.UUCP]

	I had a setup where I shared a RP07 between UNIX and VMS.  What I did
was modify the VMS device driver to think the RP07 was only 500 cylinders
instead of 630.  The place where this happens was in DRDRIVER.EXE (see micro-
fiche with your distribution).  I had a little trouble figuring out the PATCH
utility but eventually got it.  Two locations need to be modified: the number
of cylinders and the number of bytes.

	What you then do is put the new DRDRIVER.EXE into sys$system and reboot.
This MUST be done on a disk other than the type you are modifying.  We did the
mods on an RM05 for our RP07.  Now VMS thinks RP07's are 500 cylinders long.
Now run BAD to restore the bad block info and then BACKUP a copy of your
favorite VMS filesystem over it.

	For unix I had to modify /sys/dev/hp.c.  This just was a table so it
was easy.  I left hp0b the same size because I didn't understand swapping code.
Also /sys/stand/hp.c needs to have a table modified so boot floopy does what is
right.  In your case it would be a boot TU58.

	What you get is a VMS filesystem on which you can't use standalone
utilities and which developes STRANGE problems if you run ANALYZE.  It seems
to be intact after running unix but I can't say for sure.

	The unix filesystem runs OK but seems to get corrupted when the VMS
disk diagnostics are run.  I suspect it has something to do with where the
"extra" bad block info is located.  When I say corrupted I mean FUBAR.

	I tried this scheme only briefly.  It is better to get another disk.

//Z\\
Jim Ziobro
rocksvax!z or ziobro.henr at parc-maxc