Memory Mirroring Mode - Acer Altos R920 Series User Manual

Memory mirroring mode

Memory mirroring is a high availability mode providing a redundant
image of the system memory. Two identical images of memory data are
maintained, providing maximum redundancy. Mirroring is achieved
across Branch 0 and Branch 1 such that one of these branches is the
primary image and the other the secondary. The memory controller
alternates between both branches for read transactions. Write
transactions are issued to both branches under normal circumstances.
Due to the available system memory being divided into a primary
image and a copy of the image, the effective system memory is
reduced by one-half. For example, if the system is operating in memory
mirroring mode and the total size of the FBDIMMs is 2 GB, the effective
size of the memory is 1 GB because half of the FBDIMMs are the
secondary images.
For memory mirroring to work, memory boards must be installed in
pairs and all DIMMs with the same slot number must match. For e.g.
Memory board A DIMM slot 1 must be the same as memory board B
DIMM slot 1. DIMMS installed must be the same number of ranks,
timing, and size.
The BIOS provides a Setup option to enable memory mirroring. When
memory mirroring is enabled, the BIOS attempts to configure the
memory system accordingly. If the FBDIMM population is not suitable
for mirroring, the BIOS disables mirroring. It then reverts to the default
non-RAS mode with maximum interleave or to the single channel
mode based on the system memory configuration. BIOS Setup then
displays the selected memory configuration on the next boot.
To configure memory to memory mirroring mode:
1 Run BIOS setup. See "Entering BIOS setup" on page 100.
2 Use the up and down arrow keys to select the Advanced menu.
3 Use the up and down arrow keys to select Memory
Configuration, then press Enter. The Memory Configuration
menu appears.
4 Use the up and down arrow keys to select Memory RAS and
Performance Configuration, then press Enter. The Memory RAS
and Performance Configuration menu appears.
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