In my first post in this series, I mentioned one of the advantages of hardware RAID is what's called battery backed cache. Rest assured, the time has finally come to explain this term. Some RAID implementations have memory installed, exactly like the RAM that's in a computer, and a battery as well. When data is to be written to the hard drives, it can be stored in the memory to protect it. In the event the computer loses power before writing the data, the onboard battery keeps the memory functional, and the data intact, for a time, hopefully long enough for power to be restored.

There are different approaches to using this, called write back and write through, but they advantages and disadvantages of each are a little more technical and subjective than I'm going to get into here.