Dell PowerEdge M820 Dell PowerEdge M820 Systems Owner's Manual - Page 54

Mode-Specific Guidelines, Advanced ECC (Lockstep), Memory Optimized (Independent Channel) Mode

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• Populate DIMMs based on the following processor-heat sink configurations. Table 2. Processor and Heat Sink Configurations Processor Configuration Processor Type (in Watts) Heat Sink Maximum Number of DIMMs Reliability, Availability, and Serviceability (RAS) Features Two processors Up to 95 W 67 mm 24 (Three DIMMs per channel) 24 (Three DIMMs per channel) Two processors Above 95 W 87 mm 20 (Three DIMMs in channels 0 and 3 and two DIMMs in channels 1 and 2) 16 (Two DIMMs per channel) Four processors Up to 95 W 67 mm 48 48 Four processors Above 95 W 87 mm 40 (Three DIMMs in channels 0 and 3 and two DIMMs in channels 1 and 2) 32 (Two DIMMs per channel) Mode-Specific Guidelines Four memory channels are allocated to each processor. The allowable configurations depend on the memory mode selected. NOTE: x4 and x8 DRAM based DIMMs can be mixed providing support for RAS features. However, all guidelines for specific RAS features must be followed. x4 DRAM based DIMMs retain Single Device Data Correction (SDDC) in memory optimized (independent channel) mode. x8 DRAM based DIMMs require Advanced ECC mode to gain SDDC. The following sections provide additional slot population guidelines for each mode. Advanced ECC (Lockstep) Advanced ECC mode extends SDDC from x4 DRAM based DIMMs to both x4 and x8 DRAMs. This protects against single DRAM chip failures during normal operation. Memory installation guidelines: • Memory modules must be identical in size, speed, and technology. • DIMMs installed in memory sockets with white release tabs must be identical and similar rule applies for sockets with black and green release tabs. This ensures that identical DIMMs are installed in matched pairs for example, A1 with A2, A3 with A4, A5 with A6, and so on. NOTE: Advanced ECC with Mirroring is not supported. Memory Optimized (Independent Channel) Mode This mode supports SDDC only for memory modules that use x4 device width and does not impose any specific slot population requirements. Memory Sparing NOTE: To use memory sparing, this feature must be enabled in the System Setup. In this mode, one rank per channel is reserved as a spare. If persistent correctable errors are detected on a rank, the data from this rank is copied to the spare rank and the failed rank is disabled. With memory sparing enabled, the system memory available to the operating system is reduced by one rank per channel. For example, in a dual-processor configuration with sixteen 4 GB dual-rank DIMMs, the available system memory is: 3/4 (ranks/channel) × 16 (DIMMs) × 4 GB = 48 GB, and not 16 (DIMMs) × 4 GB = 64 GB. 54

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•
Populate DIMMs based on the following processor-heat sink configurations.
Table 2. Processor and Heat Sink Configurations
Processor
Configuration
Processor
Type (in
Watts)
Heat
Sink
Number of DIMMs
Maximum
Reliability, Availability, and
Serviceability (RAS) Features
Two processors
Up to 95 W
67 mm
24 (Three DIMMs per
channel)
24 (Three DIMMs per channel)
Two processors
Above 95
W
87 mm
20 (Three DIMMs in
channels 0 and 3 and two
DIMMs in channels 1 and 2)
16 (Two DIMMs per channel)
Four processors
Up to 95 W
67 mm
48
48
Four processors
Above 95
W
87 mm
40 (Three DIMMs in
channels 0 and 3 and two
DIMMs in channels 1 and 2)
32 (Two DIMMs per channel)
Mode-Specific Guidelines
Four memory channels are allocated to each processor. The allowable configurations depend on the memory mode
selected.
NOTE:
x4 and x8 DRAM based DIMMs can be mixed providing support for RAS features. However, all guidelines for
specific RAS features must be followed. x4 DRAM based DIMMs retain Single Device Data Correction (SDDC) in
memory optimized (independent channel) mode. x8 DRAM based DIMMs require Advanced ECC mode to gain
SDDC.
The following sections provide additional slot population guidelines for each mode.
Advanced ECC (Lockstep)
Advanced ECC mode extends SDDC from x4 DRAM based DIMMs to both x4 and x8 DRAMs. This protects against single
DRAM chip failures during normal operation.
Memory installation guidelines:
•
Memory modules must be identical in size, speed, and technology.
•
DIMMs installed in memory sockets with white release tabs must be identical and similar rule applies for
sockets with black and green release tabs. This ensures that identical DIMMs are installed in matched pairs -
for example, A1 with A2, A3 with A4, A5 with A6, and so on.
NOTE:
Advanced ECC with Mirroring is not supported.
Memory Optimized (Independent Channel) Mode
This mode supports SDDC only for memory modules that use x4 device width and does not impose any specific slot
population requirements.
Memory Sparing
NOTE:
To use memory sparing, this feature must be enabled in the System Setup.
In this mode, one rank per channel is reserved as a spare. If persistent correctable errors are detected on a rank, the
data from this rank is copied to the spare rank and the failed rank is disabled.
With memory sparing enabled, the system memory available to the operating system is reduced by one rank per
channel. For example, in a dual-processor configuration with sixteen 4 GB dual-rank DIMMs, the available system
memory is: 3/4 (ranks/channel) × 16 (DIMMs) × 4 GB = 48 GB, and not 16 (DIMMs) × 4 GB = 64 GB.
54