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sysgen parameter shadow_hbmm_rtc


sysgen parameter shadow_hbmm_rtc


Would anyone be able to give me a description of the sysgen parameter SHADOW_HBMM_RTC, I believe it was introduced in OpenVMS 7.3-2.

It doesn't seem to be listed in the help menu and I can't find a documented description of it.

Thanks in advance
John Gillings
Honored Contributor

Re: sysgen parameter shadow_hbmm_rtc


Generally speaking "undocumented" = "unsupported". Engineers will sometimes try to get SYSGEN parameters added to the system before they're operational. So, regardless of what you think a SYSGEN parameter might do, or how useful it might sound, if it's not documented, I'd STRONGLY recommend leaving it alone.

I'm not sure when (or if) this parameter will be activated. The intention is to use it as a timer which (in effect) controls the size of the bitmap for Host Based Mini Merge (HBMM). Until it's formally documented, please don't mess with it!

The Host Based Mini Merge manual should be released soon...
A crucible of informative mistakes

Re: sysgen parameter shadow_hbmm_rtc

Thanks John,

The reason I ask was that I performed an upgrade to OpenVMS 7.3-2 on a Server / Client cluster configuration. The server would boot up fine, however upon boot up on the client it displayed:

SYSBOOT-W-SETMAX, value set to maximum for parameter SHADOW_HBMM_RTC then after all the network interfaces were assigned I got the error message "error opening input file sys$input, error in device name or inapproproate device type. Booting it to the sysboot prompt a set the parameter back to itws default of 150 and continued but it still failed to boot. By using the default in sysboot I was able to boot it.

I could boot either machine as the server which wasn't reporting this parameter.

Not sure whether this parameter was the problem, but reverted back to v73-1 and entered MAX_SHADOW_HBMM_RTC=150 into modparams.dat then performed the upgrade with no issues.

Tim Hughes_3

Re: sysgen parameter shadow_hbmm_rtc

This reply is mainly for those may GOOGLE to this thread in the future....

I suspect (personal option) that there may be a problem with HBMM install (included in update 3) that sometimes causes the /startup and shadow_hbmm_rtc parameter values to be corrupted. This results in the error message above and problems with booting. Doing a convesational boot and setting /startup to its normal value (sys$system:startup.com) allows a boot. shadow_hbmm_rtc should then be set to it default value. I've seen systems that haved booted OK to still have a bad shadow_hbmm_rtc value.

HP are investigating...


Karl Rohwedder
Honored Contributor

Re: sysgen parameter shadow_hbmm_rtc

The HELP in SYSGEN states:



SHADOW_HBMM_RTC is the interval in seconds that the system waits
between checking reset threshold values for shadow sets that have
host-based minimerge (HBMM) bitmaps. If the reset threshold has
been exceeded, the bitmap will be reset. SHADOW_HBMM_RTC is a
dynamic parameter; its range is 60 to 65535 seconds.

The default value is 150 seconds.