Help Me Choose: 14G Memory

PowerEdge servers are very modular by nature, and you can now choose the exact quantity and type of DIMMs for your system.

• To configure your system’s memory for optimal performance, keep these best practices in mind:

1. Populate all memory channels evenly with the same rank, size, and speed of DIMMs. 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.
2. Choose the appropriate processor to support the expected memory frequency. For example, if your workload requires a memory speed of 2666MT/s, select a processor model that supports this speed.
Memory Configuration Type
Reduce data loss and keep your system online and operational with reliability, availability and serviceability (RAS) features for Dell servers and storage, including:

Memory mirroring has two adjacent memory channels configured to write the same data to each channel. If one memory channel fails or encounters an error, the other channel continues to transmit data. It’s an excellent safeguard for systems requiring uninterrupted operation, though it cuts memory capacity in half, doubles the cost per gigabyte, and can increase power consumption.

Memory sparing can reduce downtime from correctable errors by allocating one rank (64-bit wide data area on a DIMM) per channel (Single Rank Spare Mode) or two ranks per channel (Multi Rank Spare Mode) as memory spares. If a correctable error occurs in a rank or channel, it’s moved to the spare rank while the OS is running. This prevents the error from causing a failure. Memory sparing reduces memory capacity by one rank per channel or two ranks per channel (depending if Single Rank or Multi Rank is selected) and increases the cost per gigabyte.

DIMM Type
Choose from three different dual in-line memory module types or DIMM types that can meet your needs depending on how your prioritize R.A.S. (reliability, availability, and serviceability) and power consumption (there are limitations per platform).

Dell is supporting three DIMM types:

  • RDIMM: Registered DIMM – Provides for higher capacity options and advanced RAS features.
  • LRDIMM: Load Reduced DIMM – Provides maximum capacity but higher power consumption.
  • NVDIMM: Non-Volatile DIMM – Provides a persistent memory solution with NAND and DRAM that maintains data in power loss, system crash, or normal shutdown. This solution requires a battery as a power source for an AC loss condition.


RDIMM
, or registered memory, is the most commonly used DIMM type, and offers the best mix of frequency, capacity, and rank structure choices. It provides high signal integrity — performing parity checking to detect improper addresses or commands — and increased performance for heavy workloads.

RDIMMs (Single Rank and Dual Rank)

  • Maximum frequency of 2666 MT/s
  • Maximum frequency using 2 DIMMs per channel of 2666 MT/s
  • Maximum capacity of 32GB per DIMM
  • Maximum system capacity of 768 GB

 
LRDIMM
, or load-reduced memory, uses a buffer to reduce memory loading to a single load on all DDR signals, allowing for greater density.

LRDIMMs

  • Maximum frequency of 2666MT/s
  • Maximum frequency using 2 DIMMs per channel of 2666MT/s
  • Maximum capacity of 128GB per DIMM
  • Maximum system capacity of 3TB


NVDIMM- N
is a nonvolatile persistent memory solution that combines NAND flash and DRAM. "Non-volatile" means that the memory retains its contents even when electrical power is removed either from an unexpected power loss or system crash.

NVDIMM-Ns

  • Maximum frequency of 2666MT/s
  • Maximum frequency using 2 DIMMs per channel of 2666MT/s
  • Maximum capacity of 16GB per DIMM
  • Maximum system capacity of 192GB (up to 12 DIMMs per system)


DIMM Speed

There is only one speed option for 14G DD4

  • 2666MT/s – DIMMS will run at 1.2 volt


RAS Feature

RAS feature options offered on these servers (these are not supported on NVDIMM-N):

  • Memory Optimized – Baseline RAS features for highest performance optimization
  • Single Rank Memory Sparing- RAS feature that allocates one rank per channel as a spare to reduce the likelihood of correctable errors from becoming uncorrectable errors but available memory capacity is reduced. This feature requires two ranks or more populated per channel.
  • Multi Rank Memory Sparing- RAS feature that allocates two ranks per channel as a spare to reduce the likelihood of correctable errors from becoming uncorrectable errors but available memory capacity is reduced. This feature requires three ranks or more populated per channel.
  • Memory Mirroring – RAS Feature with paired memory provides data and transmission fault-tolerance but available memory capacity is reduced by 50%
  • Dell Fault Resilient Memory (FRM) - This Dell-patented technology enables PowerEdge server customers supporting VMware vSphere 5.5 to maximize available server memory while increasing protection against memory faults for the hypervisor and mission critical applications.

 


DIMM Speed and Frequency
The memory offerings for Dell PowerEdge 14th-generation servers are based on the double-data rate type 4 (DDR4) which operates at 1.2 volts.

PowerEdge memory speeds by type and loading:

 DIMM Type  DIMM RankingCapacity DIMM Rated Voltage, Speed 14th Generation Memory
 1 DPC2 DPC

 RDIMM

1R/2R 

 8GB, 16GB, and 32GB

DDR4 (1.2V), 2666 

2666

2666

 LRDIMM

4R/8R 

64GB and 128GB 

DDR4 (1.2V), 2666 

2666

2666

NVDIMM

1R

16GB

DDR4 (1.2V), 2666

2666

2666



DIMM Comparison Table

The table below lists the comparison between different DIMM types.

 

     R DIMM

LR DIMM

 NVDIMM

Registered/Buffered

  Address only

Address and data

 N/A

Frequency/Speed

2666 MT/s

2666 MT/s

 2666 MT/s

Ranks Supported

1 or 2

4 or 8

 1

Capacity per DIMM

8GB, 16GB and 32GB

64GB and 128GB

 16GB

Maximum DIMM per Channel

2

 2

Dynamic RAM (DRAM) Technology

x4 and x8

x4

 x4

Temperature Sensor

Yes

Yes

 Yes

Error-Correction Code (ECC)

Yes

Yes

 Yes

 Single Device Data Correction (SDDC) – Only supported on x4 DIMMs

Yes

Yes

 Yes

Address Parity

Yes

Yes

 Yes