[Info-vax] Reconfiguring VMS 6.2 - Shadow set question

[Stephen Hoffman]

On 2012-10-23 14:22:22 +0000, Paul Sture said:

> In article <k64k7u$s9f$1 at dont-email.me>,
>  Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> 
>> On 2012-10-22 21:43:45 +0000, Jan-Erik Soderholm said:
>> 
>>> In no case do you need a MOUNT of the system disk in any command file.
>> 
>> In no case?  In any command file?  Careful with those absolutes...
>> While I understand your intent (and your statement is correct for what
>> you intend), it's quite possible to mount system disks additional times
>> for specific requirements, and there are constructs where mounting the
>> disk (shared) is handy to state (and enforce) an interest in a
>> particular disk.  Mounting a disk (shared) in a batch job means that
>> the disk won't drop offline due to an operator request, a state which
>> can be handy for data disks and for remote-mount system disks.
>> Mounting a disk a second time (during the bootstrap) can also be common
>> to bring that disk online in a cluster, too.  Now does everybody do
>> this?  No.  (A number of folks probably don't know about mounting disks
>> shared to maintain interest, but it's documented.)  And does the system
>> manager generally need to deal with mounting the local system disk in a
>> standalone configuration?  No.  But sites can choose to...
> 
> I believe Jan-Erik was referring to mount system disk shadow set members
> in the startup files.
> 
> From the Volume Shadowing Manual:
> 
> http://h71000.www7.hp.com/doc/73final/5423/5423pro_003.html
...

I know and understand what was meant.  It was correct for the specific 
case, and - following the absolute - can be incorrect for the general 
case.  As I stated in my reply.

You can MOUNT a disk multiple times.  This includes a system disk.

This as part of an application that wishes to express an "interest" in 
a mounted disk, and to effectively disallow its dismount for the 
duration of some related processing.  This mechanism is useful in batch 
jobs, particularly when disks are being mounted and dismounted in a 
comparatively active or volatile environment.

This general MOUNT sequence is mentioned here 
<http://h71000.www7.hp.com/wizard/wiz_7881.html> - but who knows who 
that wizard guy really was, and that article is clearly not part of the 
official docs...  So quoting from The Fine Manuals 
<http://h71000.www7.hp.com/doc/82final/aa-pv5mj-tk/aa-pv5mj-tk.html> - 
from the official docs:

"Using the MOUNT/SHARE command on disks already mounted with the 
/SYSTEM qualifier retains a lock on disk availability even if the disk 
is dismounted on a systemwide basis. This practice is not usually used 
for the system disk, but it can occur as a result of invoking a 
general-purpose command procedure that is sometimes used on system and 
nonsystem disks."

There are probably better and more detailed references around elsewhere 
in the OpenVMS documentation, but this is what showed up with a quick 
search.




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