Nuts & Bolts: Database Servers

We only use RAID controllers that have a battery backup for the cache, disable read-ahead caching, and turn on write-back caching. With this setup we’re able to configure MySQL to immediately flush all writes to the disk rather than relying on the operating system to periodically write the data to the drives. In reality, the writes will be staged to the controller’s cache, but with the battery backup we are protected from unexpected power outages which could otherwise cause data loss. In addition, since the controller is caching the writes in memory, it can optimize the order and number of writes that it makes to the physical disks to dramatically improve performance.
(Link: Nuts & Bolts: Database Servers)