2 TB Hard Drive (7200 RPM) Expansion Kit for WD Sentinel DS5100 and DS6100. 2 TB 7200 64M SATA3 6GB/S 24x7 reliability - With 1.2 million hours MTBF, these drives have the highest available reliability rating on a high-capacity drive. RAID-specific time-limited error recovery (TLER) - Pioneered by WD, this feature prevents drive fallout caused by the extended hard drive error-recovery processes common to desktop drives. Rotary Acceleration Feed Forward (RAFF) - Optimizes operation and performance when the drives are used in vibration-prone multi-drive systems such as rack mounted servers.