[Info-vax] question on HBVS and SHOW DEVICE

[Ken Fairfield]

On Thursday, October 3, 2013 6:26:23 AM UTC-7, Paul Sture wrote:
> In article <l2j9o9$gtv$1 at online.de>,
>  helbig at astro.multiCLOTHESvax.de (Phillip Helbig---undress to reply) 
>  wrote:
> 
> > Consider the output from SHOW DEVICE/FULL below.  Question: why does the 
> > "shadow set virtual unit" appear for one of the disks but not the other 
> > two?  (For what it's worth, all disks are physically identical.)
> > 
> > Does it appear if the disk (shadow member) in question does not have a 
> > direct connection to the node on which the command is issued?
> > 
> > Disk DSA510:, device type Generic SCSI disk, is online, mounted, 
> > file-oriented
> >     device, shareable, available to cluster, error logging is enabled, device
> >     supports bitmaps (bitmaps active).
> > 
> 
> <snip>, physical volumes follow:
> 
> >   Volume is also mounted on LEEBIG, MINNIM.
> > 
> > Disk $110$DKB400:, device type DEC RZ2ED-LS, is online, member of shadow set
> >     DSA510:, served to cluster via MSCP Server, error logging is enabled.
> > 
> >     Error count                    2    Shadow member operation count   
> >     3462353
> >     Allocation class             110
> > 
> > Disk $150$DKB400:, device type DEC RZ2ED-LS, is online, member of shadow set
> >     DSA510:, shadow set virtual unit, error logging is enabled.
> > 
> >     Error count                    0    Shadow member operation count    
> >     615995 
> >     Current preferred CPU Id       0    Fastpath                              
> >     1
> >     Host name               "LEEBIG"    Host type, avail Digital Personal 
> >     WorkStation , yes
> >     Allocation class             150
> > 
> > Disk $170$DKB400:, device type DEC RZ2ED-LS, is online, member of shadow set
> >     DSA510:, shadow set virtual unit, error logging is enabled.
> > 
> >     Error count                    0    Shadow member operation count    
> >     618930
> >     Current preferred CPU Id       0    Fastpath                              
> >     1
> >     Host name               "MINNIM"    Host type, avail Digital Personal 
> >     WorkStation , yes
> >     Allocation class             170
> 
> Correction: "shadow set virtual unit" appears for the last 2 disks 
> listed but not the first.  The first disk is "served to cluster via MSCP 
> Server" which implies that there is a direct path from the host to the 
> second and third disks but the first is physically connected to another 
> system and is visible via MSCP.

Almost, Paul.  The 2nd and 3rd units, alloclass $150$ and $170$,
are MSCP-served to the host doing the SHOW DEVICE.  That's why
their output includes a "Host name" line.   

The key here is that the output varies depending upon whether
the disk in question is locally attached or accessed via MCSP.
The choice of what particular text gets displayed was simply a
decision of the VMS Engineers who wrote the code, eh?  I would
have thought Phillip would have figured that out pretty quickly 
since he's intimately familiar with his cluster...

    -Ken