IBM X3950 X5 Problem Determination And Service Manual page 27

Table 3. x3850 X5 Memory RAS Features (continued)
Nodes Hemisphere
Mode
(DIMM
configuration
match
between
both CPU
memory
controllers)
(Note 1)
2 nodes (QPI Required for
scaling) QPI scaled
2-node.
Unmatched
memory is
discarded to
enable
Hemisphere
Mode on all
installed
CPUs
2 nodes and Not required
MXA5 (EXA for EXA
scaling) 2-node. Auto
enabled
when
conditions
met on all
installed
CPUs; always
enabled on
MAX5.
Notes:
1. Hemisphere Mode
a. Both memory controllers in a CPU have the same DIMM configuration;
improves performance 16-56%.
b. UEFI automatically enables CPU Hemisphere mode when all installed CPUs
meet the requirement.
c. Memory configurations from one CPU to another need not match.
d. There is no separate UEFI Setup setting for Hemisphere mode.
e. CPU Hemisphere Mode is disabled when Memory Sparing (DIMM sparing)
or Mirroring is enabled in UEFI Setup.
f. At least 4 DIMMs per CPU are required for Hemisphere mode, but 8
DIMMs per CPU is better because it avoids a 50% performance loss.
g. Hemisphere mode is required for 8 socket QPI scaled (non EXA MAX5)
configuration (Memory Sparing/Mirroring Settings are ignored).
h. Hemisphere mode is not required in an 8 socket EXA scaled (via MAX5).
Each node would auto enable Hemisphere Mode in it's CPUs based on the
CPU memory configurations in that node alone.
i. MAX5 memory is always in Hemisphere Mode, irrespective of the CPU
Hemisphere Mode.
Memory DIMM
Mirroring Sparing (2
(Note 2) DIMMs
spare per
memory
card) (Note
3)
Not Not
supported supported
CPU Enabled by
Intrasocket UEFI setting
and MAX5 when
mirroring conditions
enabled by met.
UEFI setting. Unsupported
in MAX5
memory.
DDDC RBS Sparing
Sparing (1 x4 (1 x4 DRAM
DRAM spare spare per
per DIMM DIMM pair)
pair) (Note 4) (Note 5)
Auto enabled Not
for x4 supported
memory
controlled by
Westmere-EX
CPUs.
Auto enabled Auto enabled
for x4 in MAX5
memory with x4
controlled by DIMMs.
Westmere-EX
CPUs.
Chapter 2. Introduction
11