Pair of DS5400's with cross-mounted RA90's in AB mode

[Ian! D. Allen [CGL]]

Is what I'm doing here safe?

I have a pair of DS5400 machines, each with a pair of RA90's and a
pair of controllers.  They connect as expected:

    I mount cabinet 0 disk 0 port A on controller 0 of cpu0
    I mount cabinet 0 disk 1 port A on controller 1 of cpu0

    I mount cabinet 1 disk 0 port A on controller 0 of cpu1
    I mount cabinet 1 disk 1 port A on controller 1 of cpu1

That's the main stuff; each machine is connected to its to local disks. 
Now for the cross-mount in case of failure of one of the cpu's:

    I mount cabinet 0 disk 0 port B as the second disk on controller 1 of cpu1
    I mount cabinet 0 disk 1 port B as the second disk on controller 0 of cpu1

    I mount cabinet 1 disk 0 port B as the second disk on controller 1 of cpu0
    I mount cabinet 1 disk 1 port B as the second disk on controller 0 of cpu0

Thus, each disk is connected to each cpu; each controller has one
disk named "0" and one disk named "1".

If I leave all the RA90 "AB" switches both enabled, booting either 5400
alone lets it find all four disks, which are configured as ra0, ra1,
ra2, ra3.  Once one 5400 has found all four disks, it mounts the local
two in its cabinet.  If I then boot the second 5400, it only finds the
remaining two unmounted disks (which are in its cabinet), but not the
two disks mounted by the first 5400.  If I then shut down the first
5400, the second 5400 suddenly (without even a reboot) finds the two
external disks and prints a message to that effect on its console.
Booting the first 5400 again, it only finds its two local disks
(because the second 5400 has its local two mounted).

My question is: is giving each 5400 access simultaneously to a disk going
to cause problems, even though I don't actually mount any disk on more
than one CPU?  That is, should I be running with both AB switches
enabled, or should I really only enable access to one cpu at a time?

Having both AB enabled is a great convenience, since I don't have to
be physically at the machine to push buttons and switch disks over if one
cpu fails; I just mount the other disks.  But is letting both kernels
know about the disks at the same time safe?
-- 
-IAN! (Ian! D. Allen) idallen at watcgl.uwaterloo.ca idallen at watcgl.waterloo.edu
 [129.97.128.64]  Computer Graphics Lab/University of Waterloo/Ontario/Canada