Battery-Backed Write Caches
Write barriers are also unnecessary whenever the system uses hardware RAID controllers with battery-backed write cache. If the system is equipped with such controllers and if its component drives have write caches disabled, the controller acts as a write-through cache; this informs the kernel that the write cache data survives a power loss.
Most controllers use vendor-specific tools to query and manipulate target drives. For example, the LSI Megaraid SAS controller uses a battery-backed write cache; this type of controller requires the
MegaCli64 tool to manage target drives. To show the state of all back-end drives for LSI Megaraid SAS, use:
To disable the write cache of all back-end drives for LSI Megaraid SAS, use: