[Info-vax] Unpleasant Disk Shadowing Surprise

[Bob Koehler]

In article <j74n5m$vou$1 at online.de>, helbig at astro.multiCLOTHESvax.de (Phillip Helbig---undress to reply) writes:
> 
> For some definitions of "seamlessly".  I once had a system disk crash,
> back when I didn't have it shadowed (how I could sleep at night then I
> don't know).  VMS continued fine---no problems until it had to access
> the disk.

   I once had someonell the wrong platter out of our set of RP06
   drives, the system disk by mistake, and VMS went on just fine.

   It did start logging errors to OPCOM when it couldn't write to
   errlog.sys, and then when it couldn't write to operator.log, ...

> 
> SYSMAN> do write sys$output f$getsyi("boottime")
> %SYSMAN-I-OUTPUT, command execution on node MINNIM
> 11-OCT-2011 22:19:51.00
> %SYSMAN-I-OUTPUT, command execution on node JANDER
> 11-OCT-2011 22:25:38.00
> %SYSMAN-I-OUTPUT, command execution on node LEEBIG
>  1-JAN-2015 00:06:43.00
> SYSMAN> conf sh time
> System time on node MINNIM: 12-OCT-2011 20:39:17.32
> System time on node JANDER: 12-OCT-2011 20:39:17.55
> System time on node LEEBIG: 12-OCT-2011 20:39:17.74
> SYSMAN> conf set time
> SYSMAN> conf sh time
> System time on node MINNIM: 12-OCT-2011 20:39:25.88
> System time on node JANDER: 12-OCT-2011 20:39:25.90
> System time on node LEEBIG: 12-OCT-2011 20:39:25.91
> SYSMAN> do write sys$output f$getsyi("boottime")
> %SYSMAN-I-OUTPUT, command execution on node MINNIM
> 11-OCT-2011 22:19:51.00
> %SYSMAN-I-OUTPUT, command execution on node JANDER
> 11-OCT-2011 22:25:38.00
> %SYSMAN-I-OUTPUT, command execution on node LEEBIG
>  1-JAN-2015 00:06:43.00
> 
> Both the date and the time are way off for LEEBIG.  How could this 
> possibly happen?
> 

   When VMS does a normal shutdown, it writes the current time into the
   system image on the boot disk.  It also updates the hardware clock.

   When VMS boots, it reads the time out of the system image on the
   boot disk.  Depending on whether it has a "sane" match with the
   hardware clock (time on disk earlier than time on hardware clock), and 
   depending on a SYSGEN parameter that almost no one ever changes, 
   it will prompt for the time only if it doesn't trust the hardware clock.

   The 11/780 had only an 18 month "time of year" hardware clock.  Since
   I was working with 11/780 which served different configurations with
   different platter sets, the above approach would cause a prompt for the 
   time in January when we changed disks.  DEC went to off the shelf watch 
   chips in later VAXen, and IIRC Alphas always had an off the shelf
   watch chip.

   Sounds like your hardware clock somehow get set to 2015 between boots.