Table 7. Memory mirroring DIMM functionsGroup Active DIMMs Mirroring DIMMs1 1, 3 5, 72 2, 4 6, 8v The server supports online-spare memory. This feature disables the failedmemory from the system configuration and activates an online-spare pair ofDIMMs to replace the failed active DIMM pair. Online-spare memory reduces theamount of available memory. Before you can enable this feature, you must installup to two additional pairs of DIMMs. The online-spare DIMM pairs must be thesame speed, type, and the same size as, or larger than, the largest active DIMMpairs.Enable online-spare memory through the Configuration/Setup Utility program.The BIOS code assigns the online-spare DIMM pairs according to your DIMMconfiguration. Two online-spare configurations are supported. See Table 8 for theonline-spare memory DIMM connector assignments.Table 8. Online-spare DIMM connector assignmentsGroup DIMM connectors1 1 and 3, 2 and 42 5 and 7, 6 and 8v You can enable either online-spare memory or memory mirroring, but not both atthe same time. Online-spare memory provides more memory capacity thanmirroring; mirroring provides better memory protection but less memory capacitythan online-spare memory.v When you install or remove DIMMs, the server configuration informationchanges. When you restart the server, the system displays a message thatindicates that the memory configuration has changed.To install a DIMM, complete the following steps:1. Read the safety information that begins on page “Safety” on page vii and“Installation guidelines” on page 95.2. Turn off the server and peripheral devices and disconnect the power cords andall external cables, if necessary.3. Remove the server cover.Attention: To avoid breaking the retaining clips or damaging the DIMMconnectors, open and close the clips gently.4. Open the retaining clip on each end of the DIMM connector.112 IBM System x3550 Type 7978 and 1913: Problem Determination and Service Guide
