CompTIA Server+ SK0-005 Practice Question

The correct answer is that the RAID controller's write-back cache is turned off. RAID controllers often use a volatile memory cache to improve write performance by acknowledging a write operation as complete before the data is physically written to the disks (write-back caching). This cache is typically protected by a Battery Backup Unit (BBU). If the server experiences a power outage and the BBU is old or has failed, the controller will detect this upon reboot. As a safety precaution to prevent data loss from the unprotected cache in case of another power failure, the controller will disable write-back caching and switch to a much slower, but safer, write-through mode, where data is written directly to the disks. This behavior perfectly matches the symptoms of a sudden, drastic drop in write performance following a power event.