[Info-vax] Shadow System Disk between two Hosts

[Phillip Helbig---undress to reply]

In article <joss11$448$1 at news.belwue.de>,
gartmann at nonsense.immunbio.mpg.de (Christoph Gartmann) writes: 

> according to the manuals it should be possible to shadow a system disk between
> two nodes. 

If you have the proper hardware.

> I have to Itanium boxes, connected via ethernet and forming a
> cluster under OpenVMS 8.4. Currently each has its own system disk. Is it
> possible to have these disks form a shadow set and still have each node boot
> from a single member of this disk?

A system ALWAYS boots from a single member of a shadow set.  The shadow 
set is then rebuilt early in the boot sequence.  (I recommend specifying 
two shadow members in a list as the boot device.  I don't think more 
than 2 is possible (might depend on the console firmware), though of 
course a shadow set can have more than 2 members.)

I prefer a system disk for each boot node (shadow sets, of course) since 
one can then test things out on one system while the other continues to 
run.  If you want to avoid maintaining more than one system disk, in 
your case I would recommend configuring one as a satellite.  Your 
cluster won't work unless both members are up anyway (unless you have a 
quorum disk).  (Well, you could give one machine a majority of the 
votes, but then it will always have to be in the cluster, so it then 
isn't very flexible.)

To have two boot servers boot off the same disk, you have to have a disk 
which can have two controllers connected to it, or perhaps some sort of 
SAN.