3.9.1 About Disk Controller Batteries

The disk controllers in Exadata X4 and earlier systems have a battery-backed write cache to accelerate write performance.

Note:

This topic applies only to Exadata X4 and earlier systems, which use batteries to protect the disk controller cache.

If the battery charge capacity degrades such that the battery can no longer protect the cached data for a power loss of 48 hours or more, then the write cache is disabled and the disk controller switches to write through mode. This results in reduced write performance, but there is no data loss. Oracle Exadata Storage Servers generate an alert when battery charge capacity is insufficient or the temperature is high, and when the battery should be replaced.

Battery charge capacity degrades over time, and its life expectancy is inversely proportional to the operating temperature. The worst case life expectancy of the battery in Oracle Exadata Rack is as follows:

Inlet Ambient Temperature	Battery Lifetime
< 25 degrees Celsius (77 degrees Fahrenheit)	3 years
< 32 degrees Celsius (89.6 degrees Fahrenheit)	2 years