FAQ - Frequently Asked Questions - Knowledge Base
Why do WD hard drives drop from RAID sets intermittently?
WD1600YS, WD2500YS, WD4000YS, and WD5000YS hard drives are intermittently being dropped from a RAID set in certain applications and use environments without reporting any errors.
To solve this problem, update the firmware of the hard drives. For more details, see following FAQ at WD http://bit.ly/auJj36