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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

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March 2010

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Introduction

This paper serves as memory guidance for Dell??? 11th Generation PowerEdge??? R810, R910, and M910 servers released March 2010 using the new Intel?? Xeon?? 7500 and 6500 series processors that support DDR3 memory technology. This document explains what Dell supports and describes rules for installing memory. Examples of terminology definitions and details about performance or Reliability, Availability, and Serviceability (RAS) features are shown as follows.

Quick Reference Guide (Terminology Definitions)

DDR3 (Double Data Rate): The latest (3rd) generation of DDR DRAM; replaces DDR and DDR2 memory.

DIMM: Dual Inline Memory Module. This is the memory stick that is installed in each memory slot. It is comprised of multiple memory chips and, in some cases, registers, buffers and/or temperature sensors.

Dual Rank (DR): Two rows of DRAM comprising 64 bits of data each.

ECC (Error Checking and Correcting): This memory coding method is able to correct and identify certain types of DRAM and interface errors.

Enhanced ECC: Like ECC, but this memory coding method protects against additional memory error types including control line errors.

Hemisphere Mode: This mode allows interleaving between a processor???s two memory controllers leading to improved performance. Interleaving also adds benefits to memory thermal performance by spreading memory accesses across multiple DIMMs and reducing memory ???hot spots.???

Lock-step: Pairs of DIMMs are accessed as a single double-wide (128-data bit) DIMM, allowing more powerful error-correction codes to be used, including detecting address errors.

MC: Memory Controller

Intel 7500 Scalable Memory Buffer: Translates one Scalable Memory Interconnect (SMI) bus into two DDR3 buses. Intel Xeon 7500 and 6500 series processors must have this device to operate.

Mirror Mode (Mirroring): Two memory controllers are configured to allow the same data to be written to each. Each controller???s data is identical to the other; thus, if one fails or has multiple bit errors, there is a backup. The operating system will report half of your installed memory.

Quad Rank (QR): Four rows of DRAM comprising 64 bits of data each.

Rank: A row of DRAM devices comprising 64 bits of data per DIMM.

RAS: Reliability, Availability, and Serviceability

SDDC: Single Device Data Correction. Memory systems that utilize Single Device Data Correction can detect and correct multiple bit errors that come from a single memory chip on the DIMM.

Single Rank (SR): One row of DRAM comprising 64 bits of data.

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Sparing (DIMM and Rank): The system allocates a Rank or DIMM per channel as a Spare memory region, and is able to move a Rank or DIMM exhibiting correctable errors to the Spare while the operating system is running.

RDIMM: Registered DIMMs. Address, Control, and Clock lines are buffered and re-driven on the DIMM.

Overview Intel Architecture

PowerEdge 11Th Generation 4-socket servers use the new Intel Xeon 7500 and 6500 series processors that support DDR3 memory technology. Each processor has two memory controllers that support two Millbrook Memory Buffers. Every Millbrook Memory Buffer supports up to four DIMMs, which allows for greater scalability and memory performance.

It is important to recognize that memory speed and the processor chosen have interdependencies. The processor???s maximum QuickPath Interconnect (QPI) speed will determine the memory performance (1066 MTS, 978 MTS, or 800 MTs). Memory speed remains locked regardless of DIMM population. There is no speed change when populating increasing numbers of DIMMs. However, there are recommended population practices when upgrading or changing memory. DIMMs always must be populated identically in pairs (A1-A2, for example).

Note: Only RDIMMS are supported with Intel 7500 and 6500 series processors.

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

PowerEdge R810 and M910

The R810 and M910 servers utilize DDR3 memory providing a high performance, high-speed memory interface capable of low latency response and high throughput. The R810 and M910 support Registered DDR3 DIMMs (RDIMMs) only.

The R810 and M910 utilize Intel Xeon 7500 and 6500 series processors that have four SMI channels for each socket. Each of those memory controllers then has two SMI channels that connect to the Intel 7500 Scalable Memory Buffer.

The DDR3 memory interface consists of eight Intel 7500 Scalable Memory Buffers (two per socket), each of which has two DDR3 memory channels. Each channel supports up to two RDIMMs for single/dual/quad rank. By limiting to two DIMMs per DDR channel, the system can support quad-rank DIMMs at 1066 MTs. The R810 and M910 support a maximum of 32 DIMMS with four SMI channels per socket, two Intel 7500 Scalable Memory Buffers per SMI channel, and two DDR3 channels per memory buffer supporting two DIMMs each.

FlexMem Bridge Technology

In a four-CPU configuration, the R810 and M910 use only one memory controller per CPU. This single controller connects to two memory buffers via SMI links. Each memory buffer in turn connects to four DDR3 DIMMs with a total of 32 DIMMs accessible. In a two-CPU configuration, normally this would mean that only four memory buffers are connected; therefore, a total of only 16 DIMMs are accessible.

To overcome this limitation with two CPUs, the R810 and M910 use a pass-through, called the FlexMem Bridge, in the sockets without CPUs (CPU 3 and CPU 4). This allows CPU 1 and CPU 2 to connect to the memory of their respective adjacent sockets (CPU 3 and CPU 4) and access the additional 16 DIMMs.

The FlexMem Bridge provides the following:

???Two pass-through links for SMI

???One pass-through link for QPI

???The pass-through SMI links connect the two installed CPUs to additional Intel 7500 Scalable Memory Buffers; therefore, the CPUs will have the following memory attached:

???CPU 1 will have access to DIMMs A1-A8 and to DIMMs C1-C8 (those normally associated with CPU 3)

???CPU 2 will have access to DIMMs B1-B8 and to DIMMs D1-D8 (those normally associated with CPU 4)

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Figure 2. R810 and M910 Series Servers Memory Illustration

Note: This illustration is not a technical schematic of a motherboard. DIMMs A1-A8 correspond to CPU 1, DIMMs B1-B8 correspond to CPU 2, DIMMs C1-C8 correspond to CPU 3, and DIMMs D1-D8 correspond to CPU 4.

PowerEdge R910

The R910 utilizes DDR3 memory providing a high performance, high-speed memory interface capable of low latency response and high throughput. The R910 supports RDIMMs only.

The R910 utilizes Intel Xeon 7500 series processors that have one memory controller hub and two integrated memory controllers. Each of those memory controllers has two SMI channels that connect to the Intel 7500 Scalable Memory Buffer.

The DDR3 memory interface consists of 16 Intel 7500 Scalable Memory Buffers, each of which has two DDR3 memory channels. Each channel supports up to two RDIMMs (single/dual/quad-rank). By limiting to two DIMMs per DDR channel, the system can support DIMMs running at 1066 MTs.

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

The R910 has eight memory risers; each memory riser has two Millbrook memory buffers and eight DIMM slots.

Figure 3. R910 Series Servers Memory Illustration

Note: This illustration is not a technical schematic of a motherboard. DIMMs in Risers A and B correspond to CPU 1, DIMMs in Risers C and D correspond to CPU 2, DIMMs in Risers E and F correspond to CPU 3, and DIMMs in Risers G and H correspond to CPU 4. A CPU must be present to populate the riser. A system can operate with only one riser per CPU.

Optimizing Memory Performance for Intel Xeon 7500 and 6500 Series Processors

Intel Xeon 7500 and 6500 Series processors support a maximum memory performance of 1066 MTs.

Best Performance

2 DIMMS per Memory Buffer Channel, all memory controllers populated equally with 64 DIMMs and 8 Memory Risers (R910) (see Figure 4) or 32 identical DIMMs (R810, M910) (see Figure 5), highest bandwidth and lowest latency

Better Performance

1 DIMM per Memory Buffer Channel, all memory controllers populated equally with 32 DIMMs and 8 Memory Risers (R910) (see Figure 6) or 16 identical DIMMS (R810, M910) (see Figure 7), slight bandwidth decrease

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Good Performance

2 DIMMS per Memory Buffer Channel, all memory controllers populated equally with 32 DIMMs and 4 Memory Risers (R910), lower maximum bandwidth, higher latency

1 DIMM per Memory Buffer Channel, all memory controllers populated equally with 16 DIMMs and 4 Memory Risers (R910), lower maximum bandwidth, higher latency

Note: Mixed DIMM capacity is supported. The recommendation is to populate memory controllers equally and always pair DIMMs identically.

Figure 4. R910 Relative Memory Bandwidth for the Intel Xeon 7500 Series Processors

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Figure 9. R810 and M910 With 16 Identical DIMMs, 1 DIMM Per Channel

Memory RAS Features

Sparing

For Rank sparing, one rank on each lock-step Millbrook pair will be reserved as a spare, and in the event that another rank exceeds a threshold of correctable ECC errors, the ???failing??? rank will be copied to the spare. After that operation is complete, the failed rank will be disabled.

For Dual rank DIMMs: 1 rank within a DIMM is used as a spare

For Quad rank DIMMs: 1 or 2 ranks within a DIMM are used as a spare

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Figure 10. Example of Sparing for Dual Rank and Quad Rank DIMMs

Mirroring

For mirroring, the R910 will support 2P/4P configurations for >= 64 GB only. The R810 and M910 support mirroring in 32 DIMM configurations >= 64 GB only. When mirroring is enabled, only half of the physical memory will be visible to the system. A full copy of the memory is maintained, and, in the event of an uncorrectable error, the system will switch over to the mirrored copy. The R910 uses intra-socket mirroring.

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PowerEdge 11th Generation Servers: R810, R910, and M910 Memory Guidance

Figure 11. Example of R910 Intra-Socket Mirroring

Note: A1, A3 are mirrored to A2, A4; B1, B3 are mirrored to B2, B4; C1, C3 are mirrored to C2, C4; D1, D3 are mirrored to D2, D4; E1, E3 are mirrored to E2, E4; F1, F3 are mirrored to F2, F4; G1, G3 are mirrored to G2, G4; H1, H3 are mirrored to H2, H4.

For mirroring, the R810 will support 2P/4P configurations with 32 DIMMs only. When mirroring is enabled, only half of the physical memory will be visible to the system software. A full copy of the memory is maintained, and, in the event of an uncorrectable error, the system will switch over to the mirrored copy. In 2P mode, the mirroring will be inter-node with hemisphere mode enabled.

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