  Dissimilar device shadowing? 
 The Question is:
 
I'm working on creating an extremely fast and highly available I/O solution
for implementation into a large CI cluster.  I was thinking about adding two
ES40's with a ram drive on each system mirrored to each other and to fibre
connected solid state disk.
  I read the DECram SPD (34.26.07) and it looks like I'm good to go with
shadowing the ram drives and MSCP serving them but there are two statements
in the SPD which appear to be contradictory.
In the restrictions it states that shadowing will support shadow sets
comprised of ram disks and other class devices in a future release, I assume
this means that it can't do it now.  There is another restriction which
states that the data is volatile and
 you will lose data if a failure occurs unless you shadow the data to a real
physical device using a supported version of volume shadowing.
The question I have is, is it legal to shadow the ram drives with solid
state on the fibre channel?
Thanks for any help or suggestions you can offer.
 
 The Answer is:
 
  Disk devices -- whether dissimilar or otherwise -- can now be shadowed
  using host-based OpenVMS Volume Shadowing, so long as all disks involved
  in the shadow set have the same total number of blocks.
 
  Support for shadowing disks with differing numbers of total blocks is
  under discussion for an OpenVMS release -- currently a release after
  the (not available at the time of this wiring) OpenVMS V7.3 release.
 
