[Info-vax] Shadow System Disk between two Hosts

[Michael Moroney]

gartmann at nonsense.immunbio.mpg.de (Christoph Gartmann) writes:

>In article <jot349$vr4$4 at online.de>, helbig at astro.multiCLOTHESvax.de (Phillip Helbig---undress to reply) writes:

>>No, he wants to boot two machines from the SAME shadow set.  Possible 
>>with fancy hardware.

>Ok, so it is not possible to have a shadow set with two disks, one connected to
>node A and the other to node B and use this one as a system disk?

The best way is shared storage, a SAN or a "scsi cluster" where 2 or 3 
hosts and one or more drives share a SCSI bus.  I don't remember if there
is supported "scsi cluster" configurations for Itanium systems.

Having said that, it is possible to do what you want, although you
really shouldn't do that.  Keith P. described it.  I have seen something
similar, two Alphas, each with their own drive that together, made a
system disk shadowset.  Each Alpha was set up as a boot server, *and* was
set up to boot over the network from the other Alpha! The SYSGEN parameter
SHADOW_SYS_TMO was set to longer than the time for a system to crash, 
write a dump and reboot to the point where it would MSCP serve its own
drive to the other system, maintaining the shadowset.  An obvious question
is quorum, I don't remember what they did to maintain it.  But each system
MSCP-served its own drive to the other, and they would maintain a 
shadowset across boots without merges.

Of course another issue was the system could not boot if both nodes were
down.  They'd have to manually boot one system from its own drive.