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
Table
Response to Various AC Power Conditions
Condition
Low line voltage
No line voltage (AC loss)
UPS
UPS power down
Response
UPS compensation circuit automatically increases output voltage, without placing load on the UPS battery.
UPS switches to the battery, which supplies power to the controller 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 signals controller of impending power down. Subsystem discontinues host services. Cache flush is completed.
UPS shuts itself off, preventing complete battery discharge. All data has been written to disk.
