You and the author of the title are confusing cache layers and "battery protection." A RAID BBU will only protect the RAID controller's write cache; the thing t

You and the author of the title are confusing cache layers and "battery protection." A RAID BBU will only protect the RAID controller's write cache; the thing that your write IO sits in until the controller flushes to the disk set. That's either 4-5 seconds depending on Dell/LSI model or until it gets pushed out for cache capacity. The above has absolutely zero to do with the drive write cache and power protection. The drive write cache is used to cache the write on the drive after the RAID controller. Spinning metal drives have caches. SSD's have caches. Whether you use the cache is up to you and your OS. The safest setting is off. You can usually get more performance by leaving it on. This is why Windows would throw warnings all over the place when enabling write caching without a connected UPS. I'm not sure exactly what the logic is on Linux for sd/sg devices. The default Dell RAID controller behavior with write caching on drives is based on drive interface. SAS = off. SATA = on. If you run non-power safe SATA drives with a Dell RAID controller, you must disable the write cache if you want data durability. Then again, you could also run your databases on power-safe, non-consumer SSD's. This whole article was basically a giant warning sign saying "run away they need serious help."