Lenovo 3821, 3822, 3719, 3823 manual Independent channel mode, Memory mirroring mode

vThe server supports 1 GB, 2 GB, and 4 GB DIMMs, with a minimum of 1 GB and a maximum of 64 GB of system memory.

For 32-bit operating systems only: Some memory is reserved for various system resources and is unavailable to the operating system. The amount of memory that is reserved for system resources depends on the operating system, the configuration of the server, and the configured PCI devices.

vThe maximum operating speed of the server is determined by the slowest DIMM in the server.

vThe server can operate in two major modes: mirroring and independent channel modes.

Independent channel mode

The server requires at least one installed DIMM per microprocessor. The server comes with a minimum of two 1 GB DIMMs, installed in connectors 3 and 6. Connector 3 (in channel 0) and connector 6 (in channel 1) are the farthest connectors from microprocessor 1 in those channels. When you install additional DIMMs, install them in the order shown in Table 11, to maintain server performance.

Note: If you have configured the server to use memory mirroring, do not use the order shown in this table; go to Table 13 on page 214 and use the installation order shown there.

Table 11. DIMM installation sequence for independent channel mode

Installed microprocessors	DIMM connector population sequence
Microprocessor 1	3, 6, 8, 2, 5, 7, 1, 4
Microprocessor 2	11, 14, 16, 10, 13, 15, 9, 12

Memory mirroring mode

Memory-mirroring mode replicates and stores data on two pairs of DIMMs within two channels simultaneously. If a failure occurs, the memory controller switches from the primary pair of memory DIMMs to the backup pair of DIMMs. You must enable memory mirroring through the Setup Utility. For details about enabling memory mirroring, see “Using the Setup Utility” on page 252. When you use the memory mirroring feature, consider the following information:

vWhen you use memory mirroring, you must install a pair of DIMMs at a time. One DIMM must be in channel 0, and the mirroring DIMM must be in the same connector in channel 1. The two DIMMs in each pair must be identical in size, type, rank (single, dual, or quad), and organization. They do not have to be identical in speed. The channels run at the speed of the slowest DIMM in any of the channels. See Table 13 on page 214 for the DIMM connectors that are in each pair.

vChannel 2, DIMM connectors 7, 8, 15, and 16 are not used in memory-mirroring mode.

vThe maximum available memory is reduced to half of the installed memory when memory mirroring is enabled. For example, if you install 64 GB of memory, only 32 GB of addressable memory is available when you use memory mirroring.

The following illustration shows the memory channel interface layout with the DIMM installation sequence for mirroring mode. The numbers within the boxes indicate the DIMM population sequence in pairs within the channels, and the numbers next to the boxes indicate the DIMM connectors within the channels. For example, the

212ThinkServer TD200x Types 3719, 3821, 3822, and 3823: Hardware Maintenance Manual