FUA (Force Unit Access). The FUA bit is a way that the RAID controller or a program (such as a database program) can ensure that data is actually written to the disk drive media, and is not stored in cache. When a write command has the FUA bit set, then the disk drive will only issue “command complete” to the controller once the data is written to media. When performance is considered more important than protection, it may be desirable to ignore the FUA bit.

Write Journaling. Write journaling tracks the writing of data to disk and preserves a copy of data that has not yet been written to the disk media. Following a power failure or in the event of accidental drive removal and reinsertion, the firmware can recover the unit without data loss. All pending writes sitting in the controller cache are replayed after power is restored or the drive is reinserted and are flushed from the controller to the drive.

Write cache disabled on degrade. In the event that a unit degrades, the use of write cache can be disabled until the unit is rebuilt. Once the unit is rebuilt, the write cache will automatically be re-enabled.