Memory Considerations; Local Memory Installation Considerations - IBM System x3850 X5 Implementation Manual

Memory installed
Both processors 1 and 2 are installed
Memory installed only on the system
board (no memory mezzanine).
Minimum of 2 DIMMs.
Memory installed on both the system
board and the mezzanine memory
board.
Memory installed on the system
board, the mezzanine memory board,
and the MAX5.

7.3 Memory considerations

Section 4.8, "Memory" on page 131 covers all of the various technical considerations
regarding memory configuration for the System x3690 X5. There is a great deal of flexibility
regarding the memory configuration of this server. As a result, there is a chance that you
might configure a less than optimal memory environment.
Before you begin this section, understand how you are going to use the server. File servers
that are used to provide access to disk storage for other servers or workstations are less
affected by a less perfect memory latency speed than a database or mail server. Servers that
are used as processing nodes in a high-performance cluster, database servers, or print
servers for graphics printers require the best memory performance possible.

7.3.1 Local memory installation considerations

The following list describes considerations when installing memory inside the System x3690
X5:
When installing memory for two processors and no mezzanine, only processing threads
assigned to processor 2 will experience a 50% increase in memory latency. For a server
with heavy I/O processing, this latency does not degrade the overall performance of the
server.
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IBM eX5 Implementation Guide
Operational characteristics
Performance improves as DIMMs are added to evenly
populate all ranks on each memory controller.
Processing threads assigned to processor 2 will always
have a significant drop in performance for
memory-intensive tasks.
Not an operational configuration for OSs, such as
VMware.
Performance improves as DIMMs are added to evenly
populate all ranks on each memory controller.
If processor 2 fails, memory on the memory mezzanine
board is unusable.
This configuration is only an operational configuration
for VMware when both the system board and mezzanine
memory board have the exact same total memory
installed. For ease of maintenance, the best practice is
to have an identical memory configuration on both the
system and mezzanine memory board.
Performance improves as DIMMs are added to evenly
populate all ranks on each memory controller for local
memory.
Performance is significantly improved when more active
memory calls are using local memory on the system
board instead of the memory located in the MAX5.
In the rare instance of a mezzanine failure, VMware
operational requirements can be satisfied if all of the
memory is installed in the MAX5. Memory access will be
significantly slower if all of the memory is in the MAX5.