IBM System Storage DS3000 Programming Manual page 529

v The controller CRU in slot B has only its Service Action Required indicator light on, but its Service
Action Allowed indicator light is off.
v After the failed power-fan CRU has been replaced, the Service Action Allowed indicator light comes on
for the controller CRU in slot B.
For more information about the Service Action Not Allowed indicator, please see the IBM System Storage
DSxxxx Storage Subsystem Installation, User's and Maintenance Guide for your storage subsystem product.
Chapter 11. Maintaining a storage subsystem
11-17