Backup Power Management - Compaq StorageWorks TM RAID Array 3000 Pedestal Storage Subsystem Hardware User's Manual

2-22 RAID Array 3000 Pedestal Storage Subsystem Hardware User's Guide

Backup Power Management

The controller must be connected to a backup battery and/or UPS to prevent
the subsystem cache from being corrupted during unexpected losses of power.
If no backup power supply is provided, the controller will remain off line and
reject all I/O requests with a status of Check Condition/Hardware Error.
If the backup power source indicates that power may be failing, the
controller's first step is to sound an alarm, enter write through mode and begin
flushing cache. If the backup power source reaches a critical state, the alarm
frequency increases and all host channels are disabled to prevent new requests
from interfering with the cache flush.
Table 2–6 lists how the controller reacts to the power supplies.
Response to Various AC Power Conditions
Condition Response
Low line voltage UPS compensation circuit automatically increases output voltage,
without placing load on the UPS battery.
No line voltage UPS switches to the battery, which supplies power to the controller
(AC loss) maintaining full functionality.
UPS signals controller of impending power down. Caching is
disabled but the controller continues to service host requests and
begins to flush cache to disk.
UPS low-battery UPS signals controller of impending power down. Subsystem
warning discontinues host services. Cache flush is completed.
UPS power down
UPS shuts itself off, preventing complete battery discharge. All data
has been written to disk.
Table 2-6