The write back cache policy for Intel® RAID Controllers can be enabled on a logical drive basis when a RAID controller cache battery backup module (BBU) is installed. The BBU will hold data in cache for a period of time in the case of a power interruption and then complete the data write to hard disk once power is returned. The amount of time the battery will hold data in cache is dependent on the controller memory and battery configuration; please check the specifications for the BBU solution being used.
If the write back setting is enabled in Intel® RAID BIOS Console 2 or Intel® RAID Web Console 2, the logical drive write back cache option will be temporarily set to write through during a battery recharge in order to protect data in the case of a power interruption during the charge cycle, then automatically returned to write back when the battery is fully charged.
When doing I/O performance tests, the performance test may show lower performance when the BBU is charging because of the temporary write through cache setting. For better performance metrics, please wait for the battery to be fully charged when the cache setting will be reset to write back for the logical drive.