A flat cache battery, and the ProLiant asking questions
The power had been off long enough for the cache battery to drain. When the power went back on, the controller asked the practice a question to which none of its staff could safely respond, so no one responded. Each member was copied prior to attempting other things. The array's metadata (the data about the array) was read back from those image copies. The parity rotation calculation was performed using the copies. The set was reconstructed by assembling it with nothing but copies. The entire practice database opened normally and all writes up to the final write made while the cache was functioning were accessible.