[Info-vax] Unpleasant Disk Shadowing Surprise

[Richard B. Gilbert]

On 10/11/2011 10:53 AM, tadamsmar wrote:
> This is VMS 7.3-2 on a DS10.  I am at V19.0 on patch updates (applied
> in July 2009)
>
> Our real-time application halted for more than 3 minutes.
>
> After the incident I found here was a disk error on one member of the
> shadow set.
>
> The first indication was whe the application watchdog alarm went off.
>
> According to the console log, more than 30 seconds after the watchdog
> sounded, the shadow set changed state, the offending disk went
> offline, a mount verification started and completed.
>
> Immediately after the mount verification completed, VMS started
> working again.
>
> Looks like the disk system was inaccessible for about 3 minutes and
> any process that tried to use it got
> halted somehow.
>
> Is this to be expected?  We have had VMS and disk shadowing running
> the application for 20 years or so, but I don't know that we have ever
> had a disk error while the watchdog was configured to sound, so we
> might not have noticed the halting and recovery.
>

When VMS attempts and fails to access a disk device, it will go through 
an error routine, the visible indication of which is a "Mount Verify" 
message, which means the O/S is attempting to determine if the requested 
disk is: present, powered on, in working order, mounted, etc.

When this happens you need to check if: the device is powered on, the 
device is in working order (yellow light on front panel says it's a 
hardware problem), the proper disk is installed, powered on, mounted, 
etc, etc.

Check the system error log for messages leading to enlightenment.

If you can't figure it out, and you have a service contract, log a 
hardware call. If you don't have hardware maintenance support, you can 
attempt to diagnose the problem yourself, replace the failing device(s). 
. . .