IBM FAStT500 User Guide - Page 50

that identifies the physical location of the controller in the chassis: controller slot A (top) or controller slot B (bottom). Each controller CRU has ten indicator lights: one power, one fault, and eight status indicator lights, as shown in the following figure. Fault Power Status lights Figure 15. Controller indicator lights Servicing notes Consider the following when servicing the controllers in the controller unit: • The controller unit supports two controller CRUs, which attach to hosts through Fibre Channel connections. • You can hot swap or replace a failed controller while the controller unit is in operation as long as the failed controller is one of a redundant pair (two controllers attached to the same host) and has a "passive" or "offline" status in the storage-management software. • If cache mirroring is enabled in redundant controllers and one controller fails, the second controller assumes processing functions without data loss. However, some or all data might be lost if cache mirroring is disabled and a failure occurs before data is written from cache memory to disk. • If you replace the controller CRU and still experience problems, the controller unit might have defective components or connections. Check the storage-management software for indications of other component failures. • If a controller CRU fails, the fault light on the affected controller glows. For more information about indicator lights, see "Checking the indicator lights" on page 15. • Firmware between the two controllers is automatically synchronized when you replace a controller. Replacing a failed controller When instructed by the storage-management software, replace a controller CRU using the following procedure. 30 IBM FAStT500 RAID Controller Enclosure Unit User's Guide