NonStop S-Series Operations Guide (G06.24+)

Power Failures: Preparation and Recovery
HP NonStop S-Series Operations Guide—522459-007
15-2
How External Devices Respond to Power Failures
The default power-fail delay time is 30 seconds, but this time can vary depending
on how your system is configured. In some circumstances, the operating system
might shorten the power-fail delay time. With a shorter power-fail delay time, the
batteries might be able to provide power to the memory for longer than the normal
45 minutes.
•
The system configuration of the enclosure
The larger the number of system components requiring power in an enclosure, the
shorter amount of time the batteries can power all the components. The size of the
system can therefore affect the configured power-fail delay time, which in turn
affects how long the batteries can maintain memory.
•
The charge state of the batteries
Properly maintaining the batteries in each enclosure and the spare batteries can
prolong the amount of time that a NonStop S-series server is able to maintain
memory during a power failure. Refer to Preparing for Power Failure on
page 15-3.
How External Devices Respond to Power
Failures
External devices, such as tape drives, external disk drives, LAN routers, and SWAN
concentrators, are not backed up by the batteries contained in an enclosure. How an
external device responds to a power failure depends on whether the device is
connected to an uninterruptible power supply.
With an Uninterruptible Power Supply (UPS)
Power to external devices, such as modular disk and tape subsystems attached to a
ServerNet/DA, continues uninterrupted during a power failure if there is a UPS for the
modular disk and tape subsystems.
Without an Uninterruptible Power Supply (UPS)
If a power failure occurs where the processors resume operations but one or more
external devices fail, data integrity problems can occur without the proper precautions.
During a power failure, a ServerNet/DA remains operational during the power-fail delay
time, but the external modular disk and tape subsystems attached to it do not. This
situation could result in data-integrity problems if the system software continues
processing data from an external disk drive or tape drive during a short power outage.
To avoid any possibility of a data-integrity problem, any time that the system software
detects a power outage, the device state for the external disk drives and tape drives is
changed to DOWN.