Help Me Choose - Memory

Help Me Choose - Memory
Dell EMC PowerEdge offers a variety of memory options to meet your workloads requirements. Memory plays a key role in your overall performance along with your processor, accelerator and storage choices.

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Properly configuring a server with balanced memory is critical to ensure memory bandwidth is maximized and latency is minimized. When server memory is configured incorrectly, unwanted variables are introduced into the memory controllers’ algorithm, which inadvertently slows down overall system performance. To mitigate this risk of reducing or even bottlenecking system performance, it is important to understand what constitutes balanced, near balanced and unbalanced memory configurations.

Variables such as DIMM consistency and slot population will dictate whether a configuration is balanced or unbalanced. Follow these guidelines at the socket and server level, to achieve a balanced memory configuration:
  1. 1
    Use 8 or 16 DIMMs per 4th Generation Intel Xeon Scalable CPU for a balanced configuration.
    Use 8 or 16 DIMMS per 5th Generation Intel Xeon Scalable CPU for a balanced configuration.
    Use 12 DIMMs per 4th Gen AMD EPYC CPU
    Use 8 or 16 DIMMs per Intel 6th Gen Xeon Scalable CPU
    Use 12 or 24 DIMMs per 5th Gen EPYC CPU
  2. 2
    Use identical DIMMs (same capacity, rank and DIMM type)
  3. 3
    Use the same memory configurations for every CPU in the server.
  4. For situations that demand mixing DIMM sizes, all memory should be chosen based on identical rank structure, and all memory channels should be populated with an identical mix of DIMM types (ie : RDIMMs cannot be mixed with LRDIMMs and Dell does not support mixing on 16G).
  5. Choose the appropriate processor to support the expected memory frequency.

Which DIMM Do I Need?

A DIMM — or dual in-line memory module — is a series of random access memory chips mounted on a small circuit board. DIMMs are installed in sockets on your computer's motherboard.

DIMM Types

RDIMM

Registered DIMM
Provides for higher capacity options and advanced RAS features. It is the most commonly used DIMM type, and offers the best mix of frequency, capacity, and rank structure choices

LRDIMM

Load Reduced DIMM
Provides maximum capacity beyond that of an RDIMM but at a higher power consumption. Uses a buffer to reduce memory loading to a single load on all DDR signals, allowing for greater capacity.

UDIMM

Unregistered or Unbuffered DIMM
Provides low latency and low density. Used on single socket servers in the PowerEdge portfolio.

Frequently Asked Questions

Intel® Optane™ Persistent Memory is a unique technology that bridges a gap between ‘memory’ and ‘storage’. Like RAM it sits within the PC memory hierarchy. By placing commonly used data and programs closer to the processor, Intel® Optane™ Persistent Memory allows the systems to access this information more quickly and improve overall system responsiveness. Intel® Optane™ Persistent Memory is designed to work in conjunction with DRAM not replace DRAM. These two memory technologies complement each other within the system. If all DIMM slots are being used, 50% of the DIMM slots will have DRAM and 50% of the DIMM slots will have Intel® Optane™ Persistent Memory.
Because of Memory Mode, Intel® Optane™ Persistent Memory can be used with almost any workload. In memory mode, the DRAM is used as a cache layer and the Intel® Optane™ Persistent Memory appears as the system memory. Any application can be used with a supported operating system. This allows a server to have a large memory footprint at a very compelling cost point. Because any application can be used, virtualization is a great use case for memory mode. Intel® Optane™ Persistent Memory is not persistent in Memory Mode.
Optimizer Mode is the default standard option for mirroring there are no special configurations.
Full Memory Mirroring allows two memory regions to be created, and a write transaction occurs in both locations to back up the data. When data is read back, if the primary copy has an ECC failure that cannot be corrected, the secondary copy is used. Full Memory Mirroring reduces capacity by half.
Each write transition is executed in two locations. Full Memory Mirroring is ideal for environments with low tolerance for memory failure & mission-critical operations. While write performance will be reduced this approach ensures a redundant copy of the data is maintained.
FRM Mode is exclusively supported in a VMware environment. It represents a variant of full memory mirroring, wherein only a portion is mirrored. Typically, a kernel is placed within this mirrored portion, providing the benefits of resiliency and the consequences of mirroring. This can be a beneficial alternative to full memory mirroring when only critical software needs the additional redundancy since it costs less than mirroring all system memory. There are no additional benefits or drawbacks.
Depending upon configuration, Idle CXL Latency is up to 300ns.
Users guide will be available on week of April 11th on the product support pages at https://www.dell.com/poweredgemanuals
Dell advises against customers installing or removing CXL AIC or DIMMs from their systems. This process can be complex and may require specialized knowledge and tools to ensure it is done correctly and safely. To avoid potential damage to the system or voiding the warranty, it is recommended to contact the Dell support team for assistance.

Useful Resources

Intel® Optane™ Persistent Memory
2nd Generation AMD EPYC™ Processors: Balanced Memory Reference Guide
How to find the supported memory configuration guide for PowerEdge Servers.
DDR5 on AMD
Dell Next Generation PowerEdge Servers: Designed with DDR5 to Deliver Future-Ready Bandwidth
Memory Bandwidth for Next-Gen PowerEdge Servers Significantly Improved with Sapphire Rapids Architecture
Balanced Memory: Intel Xeon Scalable Processors on PowerEdge Servers
DDR5 Memory Bandwidth for Next-Generation PowerEdge Servers Featuring 4th Gen AMD EPYC Processors
Memory Channel Population