NonStop NS16000 Series Planning Guide (H06.11+)

The actions that OSM takes next are directly tied to that specified ride-through time:
• If AC power is restored before the ride-through period ends, the ride-through countdown
terminates and OSM does not initiate a controlled shutdown of I/O operations and processors.
• If AC power is not restored before the ride-through period ends, OSM initiates a controlled
shutdown of I/O operations and processors by broadcasting a PFAIL_SHOUT message to all
processors (the processor running OSM being the last one in the queue) to shut down the
system's ServerNet routers and processors in a fashion designed to allow disk writes for items
that are in transit through controllers and disks to complete.
CAUTION: You should not turn off the UPS as soon as the NonStop OS is down, since the
UPS continues to provide power until its supply is exhausted, time which may be needed for
disk controllers and disks to complete disk writes.
Unlike NonStop S-series systems, this system requires a system load after a power failure that
results in system shutdown. For more information on recovering from power failures, see the
NonStop Operations Guide for H-Series and J-Series RVUs.
• Because this shutdown described above does not include powering off the system or stopping
TMF or other applications, you are encouraged to create scripts to shut down database activity
before the processors are shut down. With T0682 H02 ACC and later, OSM provides support
for automatic execution of those scripts through two OSMCONF settings:
SHUTDOWN_SCRIPT_NAME and SHUTDOWN_SCRIPT_TIME. Through these settings, you
tell OSM to execute a shutdown script a specified number of seconds before the ride-through
time is reached. OSM will not execute the script.
For more information on implementing those OSMCONF settings, see the OSM Migration
and Configuration Guide.
To configure OSM power fail support, you must perform these actions, located under the Power
Supply units in either P-switches or IOAM modules in the OSM Service Connection:
• Perform the Configure a Power Source as UPS action to configure the power rail (either A or
B) connected to the UPS.
• Perform the Configure a Power Source as AC action to configure the power rail (either B or
A) connected to AC power.
You can then perform the Verify Power Fail Configuration action, located under the System object,
to verify that power failure support has been properly configured and in place for the system.
For more information on locating or performing these actions, see the OSM Service Connection
online help.
Considerations for Ride-Through Time Configuration
Ride-through time is specified through the POWER_DELAY_TIME attribute of the SCF command
ALTER SUBSYS. For command syntax, see the SCF Reference Manual for the Kernel Subsystem.
The goal in configuring the ride-through time is to allow the maximum time for power to be restored
while at the same time allowing sufficient time for completion of disk writes for I/Os that passed
to the disk controllers before the ServerNet was shut down. Allowing enough time for sufficient
completion of these tasks allows for a relatively clean shutdown from which TMF recovery is less
time-consuming and difficult than if all power failed and disk writes did not complete. The maximum
ride-through time for each system will vary, depending on system load, configuration, and the UPS
capability.
A rack-mounted UPS can often supply five minutes of power with some extra capacity for
contingencies, provided the batteries are new and fully charged. This five minute figure is an
estimate used for illustration in this discussion, not a guarantee for any specific configuration.
You must ensure that the battery capacity for a fully-powered system allows for at least two minutes
after OSM initiates the orderly shutdown to allow the disk cache to be flushed to nonvolatile media.
Assuming the UPS has five minutes of power capacity, you would set the ride-through time for three
minutes (UPS capacity of five minutes minus two minutes for OSM).
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