Removing And Replacing Dimms - IBM xSeries 445 Type 8870 Option Installation Manual

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When memory mirroring is enabled, the data that is written to memory is stored
in two locations. One copy is kept in the memory port 1 DIMMs, while a second
copy is kept in the memory port 2 DIMMs. During the execution of the read
command, the data is read from the DIMM with the least number of reported
memory errors through Memory scrubbing, which is enabled with memory
mirroring.
If memory scrubbing determines that a DIMM is damaged beyond use, read and
write operations are redirected to the remaining good DIMMs. Memory scrubbing
then reports the damaged DIMM and the Light Path Diagnostics feature displays
the error. After the damaged DIMM is replaced, memory mirroring then copies the
mirrored data back into the new DIMM.
v Memory scrubbing is an automatic daily test of all the system memory that
detects and reports memory errors that might be developing before they cause a
server outage.
Note: Memory scrubbing and Memory ProteXion technology work with each
other and do not require memory mirroring to be enabled to work.
When an error is detected, memory scrubbing determines whether the error is
recoverable. If it is recoverable, Memory ProteXion is enabled and the data that
was stored in the damaged locations is rewritten to a new location. The error is
then reported so that preventive maintenance can be performed. Provided that
there are enough good locations to enable the correct operation of the server, no
further action is taken other than recording the error in the error logs.
If the error is not recoverable, memory scrubbing sends an error message to the
Light Path Diagnostics feature, which then lights the applicable LEDs to guide
you to the damaged DIMM. If memory mirroring is enabled, the mirrored copy of
the data in the mirrored DIMM is used to refresh the new DIMM after it is
installed.
v Memory ProteXion reassigns memory bits to new locations within memory when
recoverable errors have been detected.
When a recoverable error is found by memory scrubbing, the Memory ProteXion
feature writes the data that was to be stored in the damaged memory locations to
spare memory locations within the same DIMM.

Removing and replacing DIMMs

Complete the following steps to remove and replace a DIMM in the SMP Expansion
Module with the server turned off.
Attention:
When working with DIMMs or other options, you might need to remove
one or both of the SMP Expansion Modules. See "Hot-replace DIMMs" on page 43
for information on how to hot-replace DIMMs with the server turned on.
1. Read the safety information beginning on page v and "Installation guidelines"
on page 9.
2. Turn off the server and peripheral devices, disconnect the power cords, and all
external cables from the SMP Expansion Module.
3. Pull out on the quick release latches on each side of the server; then, pull the
server out of its rack enclosure until it stops.
4. Open the top cover.
5. If necessary, remove the top SMP Expansion Module or SMP baffle from the
server. See "Removing the SMP Expansion Module and cover" on page 32 for
instructions.
Chapter 2. Installing options
41

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