D668J: Dell PV MD3200I-3220I Controller Battery

The D668J Dell PV MD3200I-3220I Controller Battery is the backup battery unit (BBU) for the RAID controller modules of the Dell PowerVault MD3200i and MD3220i storage arrays. Each RAID controller contains a two-cell lithium-ion nanopolymer battery backup unit that powers the controller module if mains power is lost. Each controller module holds 2 GB or 4 GB of mirrored cache (4 GB is optional), protected by a battery-powered cache offload mechanism that writes the cache to non-volatile memory on power loss.

The battery is a smart BBU: it includes the battery, a battery gas gauge and a battery charger. A learn cycle discharges the battery to a threshold, then charges it back to full capacity so the gas gauge reports the charge correctly, and a new battery starts a learn cycle automatically. Learn cycles run on a regular schedule and happen simultaneously for batteries in both controller modules of a duplex array.

If the battery is missing or lacks enough charge, the controller flushes the cache and sets write-through caching for all virtual disks, and write-back is re-enabled when the battery is replaced. A battery fault lights the amber battery fault LED on the controller module. The unit sits inside the controller module, held by one screw, and is replaced by removing the controller module, opening it, sliding the battery unit along its slots and lifting it out.