two DM drives can't be used at the same time in 2.9BSD/DEMOS

[merclangrat]

I am not sure 2.9BSD or DEMOS was tested on the simulation (maybe I am the first one), but I found the following bug.

How to reproduce:

• 2.9BSD is booted from one DM (RK07) drive, e.g. /dev/hk0 - root is /dev/hk0a because BSD/DEMOS uses partitioning
• the second drive has a partition with BSD filesystem too, e.g. /dev/hk1a
• mount /dev/hk1a /mnt

then I try to copy the file: cp /etc/file /mnt
Sometimes it happens even when I run ls: ls /mnt

The system hangs. The terminal responses but it seems to be waiting for the drive. When I reboot the system, fsck shows errors - the filesystems get broken.

It works well in RT-11, for example, if I copy a file from DM1 to DM2: COPY DM1:FILE.SAV DM2 - but maybe, UNIX tries to access two drives at the same time, why it fails.
I don't have access to a real system to test, but 2.9BSD manual says directly that many drives can be used in one system - for example, hk0 can be used for / and /usr and hk1 for user data and swapping.

In case there's a bug, I can help with testing, but I have only AX4010 (F-11 with MY, DM and DW doesn't leave enough space for SignalTap).