IBM eX5 Implementation Guide

Chapter 4. IBM System x3690 X5 139

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

(

Non-Pooled 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. VMware

requires that the MAX5 memory is in

non-pooled mode.

You can change this default setting in Unified Extensible Firmware Interface (UEFI). See 7.8,

“UEFI settings” on page 337 for details.

4.8.4 Memory balance

The Xeon 7500 Series processor uses a nonuniform memory access (NUMA) architecture,

as described in 2.3.4, “Nonuniform memory architecture (NUMA)” on page 26. Because

NUMA is used, it is important to ensure that all memory controllers in the system are utilized

by configuring all processors with memory. Populating all processors in an identical fashion is

optimal to provide a balanced system and also required by VMware.

Looking at Figure 4-17 on page 140 as an example, Processor 0 has DIMMs populated, but

no DIMMs are populated that are connected to Processor 1. In this case, Processor 0 has

access to low latency local memory and high memory bandwidth. However, Processor 1 has

4 20 and 21

5

26 and 31

6

11 and 14

7

3 and 6

8

18 and 23

9

27 and 30

10

10 and 15

11

2 and 7

12

19 and 22

13

25 and 32

14

12 and 13

15

4 and 5

16

17 and 24

VMware vSphere support: MAX5 requires VMware vSphere 4.1 or later.

DIMM pair DIMM slot