NEC Express5800 User Manual page 427

The memory mirroring feature can be used under the following conditions:
Install memory devices on two memory sockets configuring a mirror set.

All the installed memory devices should have the same capacity.

Run SETUP (see Chapter 4), change parameters appropriately in the [Mirror] menu

selected as shown below, save the settings and exit from SETUP.
[Advanced] → [Memory Configuration] → [Memory RAS Mode] → [Mirror]
After SETUP finishes, rerun SETUP and make sure that the installed DIMM status is

[Mirror].
Install memory devices in the following order.

1-CPU
configuration
(Not installed)
(Not installed)
1st pair
2nd pair
1st pair
2nd pair
In 2-CPU configuration, install memory devices to the CPU2 DIMM
slots in the same order as in 1-CPU configuration.
The following mirroring cannot be configured:
Memory mirroring within a specific memory channel

Notes on Configuring Memory Mirroring
In memory mirroring configuration, [Memory RAS Mode] menu is changed from "Mirror" to
"Independent" in the following cases:
When you additionally install DIMMs that unable to configure memory mirroring

When you remove DIMMs that takes down the memory mirroring

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