>              And physically, the 3590 drives can
>be attached to multiple systems...but they can not be shared by
>multiple systems with impunity.  The problem is that an underlying
>RESERVE macro does not currently operate  across systems.

Greg - Thanks for your response on this.  One thing I don't understand is
       "RESERVE macro does not currently operate across systems".
From everything I learned from my MVS days, a Reserve is a physical hardware
latch state whose purpose is to (crudely) arbitrate access from multiple
systems.  That is, the host seeking exclusive access issues the system call
which causes the Reserve state and thus no other host can access the device.
This was quite visibily effective in S/370 devices.
    In 3590 programming in Unix, one issues an ioctl system call specifiying
SIOC_RESERVE.  If you get exclusive access, the call works; else some other
host has it, and the call fails, and you can wait for that host to do an
SIOC_RELEASE.  The device drivers manuals specifies these to be functions
for use "in a host-sharing environment".
    Reserves in general clearly work across systems: that's what they're for.
So I don't understand why ADSM could not be sure that it has exclusive rights
to a drive.  What am I missing?
       thanks, Richard Sims, Boston University OIT