An older server has performance problems writing files to a RAID array. After checking for failed drives, no problems are found. Which of the following should be checked NEXT?

A failing cooling system could cause thermal throttling of the CPU or drives, but it would not produce an isolated write performance degradation pattern without also affecting other system operations.

RAID controllers use a Battery Backup Unit to protect the write-back cache, which stages pending writes in fast DRAM before flushing them to disk, improving performance significantly. When the BBU fails or loses sufficient charge, the controller automatically falls back to write-through mode to prevent cached data loss during a power failure, eliminating the performance benefit of the cache. This is the most common cause of a sudden unexplained RAID write performance drop when no drive faults are present.

A hard drive tray failure would cause the drive to appear missing or failed in the RAID management interface, not a gradual or silent write performance reduction.

Degraded hard drive cables typically produce connectivity errors, CRC errors, or drive dropouts that would register as drive faults, not an invisible write speed reduction.