Mode-Specific Guidelines - Dell EMC PowerEdge R940xa Installation And Service Manual

Mode-specific guidelines

The configurations allowed depend on the memory mode selected in the System BIOS.
Table 15. Memory operating modes
Memory Operating Mode
Optimizer Mode
Mirror Mode
Single Rank Spare Mode
Multi Rank Spare Mode
Dell Fault Resilient Mode
Optimizer Mode
This mode supports Single Device Data Correction (SDDC) only for memory modules that use x4 device width. It does not impose any
specific slot population requirements.
94 Installing and removing system components
Description
The Optimizer Mode if enabled, the DRAM controllers operate
independently in the 64-bit mode and provide optimized memory
performance.
NOTE: DCPMM supports only Optimizer mode.
The Mirror Mode if enabled, the system maintains two identical
copies of data in memory, and the total available system memory is
one half of the total installed physical memory. Half of the installed
memory is used to mirror the active memory modules. This feature
provides maximum reliability and enables the system to continue
running even during a catastrophic memory failure by switching
over to the mirrored copy. The installation guidelines to enable
Mirror Mode require that the memory modules be identical in size,
speed, and technology, and they must be populated in sets of 6 per
processor.
Single Rank Spare Mode allocates one rank per channel as a
spare. If excessive correctable errors occur in a rank or channel,
while the operating system is running, they are moved to the spare
area to prevent errors from causing an uncorrectable failure.
Requires two or more ranks to be populated in each channel.
Multi Rank Spare Mode allocates two ranks per channel as a
spare. If excessive correctable errors occur in a rank or channel,
while the operating system is running, they are moved to the spare
area to prevent errors from causing an uncorrectable failure.
Requires three or more ranks to be populated in each channel.
With single rank 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 24x 16 GB dual-
rank memory modules, the available system memory is: 3/4 (ranks/
channel) × 24 (memory modules) × 16 GB = 288 GB, and not 24
(memory modules) × 16 GB = 384 GB. For multi rank sparing, the
multiplier changes to 1/2 (ranks/channel).
NOTE: To use memory sparing, this feature must be
enabled in the BIOS menu of System Setup.
NOTE: Memory sparing does not offer protection against
a multi-bit uncorrectable error.
The Dell Fault Resilient Mode if enabled, the BIOS creates an
area of memory that is fault resilient. This mode can be used by an
OS that supports the feature to load critical applications or enables
the OS kernel to maximize system availability.
NOTE: This feature is only supported in Gold and
Platinum Intel processors.
NOTE: Memory configuration has to be of same size
DIMM, speed, and rank.