[Info-vax] automatic shadow copy?

[Jim]

On Tuesday, March 24, 2015 at 11:56:36 PM UTC-4, IanD wrote:
> 
> I have a 7.3-2 Alpha system (ES80). Two members in the system disk shadow
> set are local disks
> 
> I was under the impression that shadow members have to be specifically
> added to the member set but when our system boots, the system disk shadow 
> member is automatically added and completes under a merge operation.
> Obviously shadow system disk is ticked in sysgen etc
> 
> I cannot find any reference to the shadow member disk anywhere in any
> procedures we run so I'm guessing that this information is embedded
> somewhere on the primary shadow member itself and that vms is
> automagically adding in the second shadow disk member of the system disk
> when it boot?
> 
> I thought this went against the recommendation that a system disk shadow
> member should not automatically be added in case it's a last known good
> copy then you have nothing to go back to? I think I read that somewhere
> 
> Any doc source that I can read up on to explain this auto adding
> phenomenon  would be great too :-)

In BITMAP.SYS there is a "storage control block" that contains sundry info
pertaining to any shadow set. One such piece of info is a list of the
current members of the shadow set. This piece of info is preserved on a
system disk when the system is shut down and then used during next boot
to re-form a shadow set with the same membership (if possible). Searching for "storage control block shadowing" will list numerous related doc
including http://h71000.www7.hp.com/doc/84final/ba554_90020/ch06s01.html .