This sets the RAID controller's write-cache policy for this virtual drive, for example write-through versus write-back. An admin picks write-back specifically for higher write performance since it acknowledges writes once they hit controller cache rather than the disk, but only trusts it with a battery/capacitor-backed cache, since a power loss before flush can lose in-flight writes under write-back. Setting this to write-back-good-bbu would enable write-back caching for this virtual drive only when the controller's battery backup is confirmed healthy.