Maximizing Memory Performance - IBM System x3850 X5 Implementation Manual

DIMM pair
9
10
11
12
13
14
15
16
MAX5 memory as seen by the operating system
MAX5 is capable of two modes of operation in terms of the way that memory is presented to
the operating system:
Memory in MAX5 can be split and assigned between the CPUs on the host system
(partitioned mode). This mode is the default.
Memory in MAX5 can be presented as a pool of space that is not assigned to any
particular CPU (pooled mode).
By default, MAX5 is set to operate in partitioned mode because certain operating systems
behave unpredictably when presented with a pool of memory space. Linux can work with
memory that is presented either as a pool or pre-assigned between CPUs, however for
performance reasons, if you are running Linux, change the setting to pooled mode.
You can change this default setting in UEFI.
VMware vSphere support: MAX5 requires VMware vSphere 4.1 or later.

3.8.3 Maximizing memory performance

In a single node x3850 X5 that is populated with four CPUs and eight memory cards, there
are a total of 16 memory buffers, as shown in the system block diagram in Figure 3-7 on
page 66. Memory buffers are listed as MB1 and MB2 on each of eight memory cards in that
diagram. Each memory buffer has two memory channels, and each channel can have a
maximum of two
maximums:
Memory cards: 8
Memory buffers: 16
Memory channels: 32
Number of DIMMs: 64
The x3850 X5 supports a variety of ways to install memory DIMMs in the eight memory cards.
However, it is important to understand that because of the layout of the SMI links, memory
buffers, and memory channels, you must install the DIMMs in the correct locations to
maximize performance.
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IBM eX5 Implementation Guide
DIMMs per channel
(DPC). A single-node x3850 X5 has the following
DIMM slots
27 and 30
10 and 15
2 and 7
19 and 22
25 and 32
12 and 13
4 and 5
17 and 24