Online-spare memory disables a failed rank pair of DIMMs from the system configuration and activates an online-spare rank pair of DIMMs to replace the failed rank pair of DIMMs. For an online-spare pair of DIMMs to be activated, you must enable this feature and have installed an additional rank pair of DIMMs of the same speed, type, size (or larger), and technology as the failed pair of DIMMs. You must enable the feature through the Configuration/Setup Utility program. To enable online-spare memory in the Configuration/Setup Utility program, select Devices and I/O Ports Advanced Chipset Control Memory Branch Mode. Use the arrow keys to change the setting for Branch 0 Rank Sparing or Branch 1 Rank Sparing to Enabled; then, save your changes. For more information, see the section about configuring the server in the User’s Guide on the IBM System x Documentation CD. When you use online-spare memory, you must consider the following information:

-You cannot enable online-spare memory while the server is operating in mirroring mode.

-When using online-spare memory the two memory branches operate independently of each other. You can enable online-spare memory for one or both branches.

-Online-spare memory reduces the amount of available memory.

-The BIOS code assigns the online-spare DIMM pairs according to your DIMM configuration.

-Online-spare memory works by copying information from a failed DIMM rank to another good DIMM rank within the same memory branch.

-Online-spare memory can not copy information from one branch to the other.

Chapter 2. Installing optional devices 13

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IBM Type 7977 manual Installing optional devices