Chapter 3. System Overview

This chapter provides an overview of the physical and architectural aspects of your SGI Altix 3700 Bx2 series system. The major components of the Altix 3700 Bx2 series systems are described and illustrated.

The Altix 3700 Bx2 series is a family of multiprocessor distributed shared memory (DSM) computer systems that initially scale from 8 to 256 Intel 64-bit processors as a cache-coherent single system image (SSI). Future releases will scale to larger processor counts for SSI applications. Contact your SGI sales or service representative for the most current information on this topic.

In a DSM system, each processor board contains memory that it shares with the other processors in the system. Because the DSM system is modular, it combines the advantages of low entry-level cost with global scalability in processors, memory, and I/O. You can install and operate the Altix 3700 Bx2 series system in a rack in your lab or server room. Each rack holds from 8 to 64 processors in 1 to 8 CR-bricks.

This chapter consists of the following sections:

Figure 3-1 shows the front views of a multiple-rack system (the Altix 3700 Bx2 system).

Figure 3-1. SGI Altix 3700 Bx2 Series Systems

SGI Altix 3700 Bx2 Series Systems

System Models

The CR-brick contains the processors (8 processors per CR-brick) and two internal high-speed routers. The routers connect to other system bricks via NUMAlink cables and expand the compute or memory capacity of the Altix 3700 Bx2. The 40U rack in this server houses all bricks, drives, and other components; up to a 64-processor configuration in a single rack. The Altix 3700 Bx2 server system can expand up to 512 Intel Itanium 2 processors, (a minimum of one IX-brick is required for every 256 processors).

The system requires a minimum of one 40U tall rack with at least one power bay and one single-phase PDU per rack. (The single-phase PDU has two openings with three cables that extend from each opening to connect to the power bay. The three-phase PDU has two openings with six cables that extend from each opening to connect to two power bays.)

You can also add additional racks containing CR-bricks, I/O bricks, and disk storage to your server system.

Figure 3-2 shows an example configuration of a 64-processor Altix 3700 Bx2 server.

Figure 3-2. SGI Altix 3700 Bx2 Server System (Example Configuration)

SGI Altix 3700 Bx2 Server 
System (Example Configuration)

System Architecture

The Altix 3700 Bx2 computer system is based on a distributed shared memory (DSM) architecture. The system uses a global-address-space, cache-coherent multiprocessor that scales to 64 Intel Itanium 2 processors in a single rack. Because it is modular, the DSM combines the advantages of low entry cost with the ability to scale processors, memory, and I/O independently to a maximum of 256 processors on a single-system image (SSI) at initial release. Larger SSI configurations may be offered in the future, contact your SGI sales or service representative for information.

The system architecture for the Altix 3700 Bx2 system is a fourth-generation NUMAflex DSM architecture known as NUMAlink-4. In the NUMAlink-4 architecture, all processors and memory are tied together into a single logical system with special crossbar switches (routers). This combination of processors, memory, and crossbar switches constitute the interconnect fabric called NUMAlink. There are two router switches in each CR-brick.

The basic building block for the NUMAlink interconnect is the CR-brick. A CR-brick contains up to four processor nodes; each processor node consists of a Super-Hub (SHub) ASIC and two 64-bit processors with three levels of on-chip secondary caches. The two Intel 64-bit processors are connected to the SHUB ASIC via a single high-speed front side bus.

The SHub ASIC is the heart of the CR-brick. This specialized ASIC acts as a crossbar between the processors, local SDRAM memory, the network interface, and the I/O interface. The SHub ASIC memory interface enables any processor in the system to access the memory of all processors in the system. Its I/O interface connects processors to system I/O, which allows every processor in a system direct access to every I/O slot in the system.

Another component of the NUMAlink-4 architecture is the router ASIC. The router ASIC is a custom designed 8-port crossbar ASIC in the CR-brick. Using the router ASICs with highly specialized NUMAlink-4 cables provides a high-bandwidth, extremely low-latency interconnect between all CR-bricks in the system. This interconnection can create a single contiguous system memory of up to 6 TB (terabytes) for a 512 processor system.

Figure 3-3 shows a functional block diagram of the Altix 3700 Bx2 series system CR-brick including nodes, routers, and other major components.

Figure 3-3. Functional Block Diagram of CR-brick

Functional Block Diagram of CR-brick

System Features

The main features of the Altix 3700 Bx2 series server systems are introduced in the following sections:

Modularity and Scalability

The Altix 3700 Bx2 series systems are modular systems. The components are housed in building blocks referred to as bricks. You can add different brick types to a system to achieve the desired system configuration. You can easily configure systems around processing capability, I/O capability, memory size, or storage capacity. You place individual bricks that create the basic functionality (compute/memory, I/O, and power) into custom 19-inch racks. The air-cooled system has redundant, hot-swap fans at the brick level and redundant, hot-swap power supplies at the rack level.

Distributed Shared Memory (DSM)

In the Altix 3700 Bx2 series server, memory is physically distributed among the CR-bricks (compute/router nodes); however, it is accessible to and shared by all CR-bricks within the system. A CR-brick with configured memory but zero processors is generally referred to as a “memory node” or M-brick.

Note the following types of memory:

  • If a processor accesses memory that is connected to the same SHUB ASIC on a compute node, the memory is referred to as the node's local memory.

  • If processors access memory located in other nodes, the memory is referred to as remote memory.

  • The total memory within the system is referred to as global memory.

Memory latency is the amount of time required for a processor to retrieve data from memory. Memory latency is lowest when a processor accesses local memory.

Distributed Shared I/O

Like DSM, I/O devices are distributed among the compute nodes (each compute node has two I/O ports) and are accessible by all compute nodes through the NUMAlink interconnect fabric.

ccNUMA Architecture

As the name implies, the cache-coherent non-uniform memory access (ccNUMA) architecture has two parts, cache coherency and nonuniform memory access, which are discussed in the sections that follow.

Cache Coherency

The Altix 3700 Bx2 server series use caches to reduce memory latency. Although data exists in local or remote memory, copies of the data can exist in various processor caches throughout the system. Cache coherency keeps the cached copies consistent.

To keep the copies consistent, the ccNUMA architecture uses directory-based coherence protocol. In directory-based coherence protocol, each block of memory (128 bytes) has an entry in a table that is referred to as a directory. Like the blocks of memory that they represent, the directories are distributed among the compute nodes. A block of memory is also referred to as a cache line.

Each directory entry indicates the state of the memory block that it represents. For example, when the block is not cached, it is in an unowned state. When only one processor has a copy of the memory block, it is in an exclusive state. And when more than one processor has a copy of the block, it is in a shared state; a bit vector indicates which caches contain a copy.

When a processor modifies a block of data, the processors that have the same block of data in their caches must be notified of the modification. The Altix 3700 Bx2 server series use an invalidation method to maintain cache coherence. The invalidation method purges all unmodified copies of the block of data, and the processor that wants to modify the block receives exclusive ownership of the block.

Non-uniform Memory Access (NUMA)

In DSM systems, memory is physically located at various distances from the processors. As a result, memory access times (latencies) are different or “non-uniform.” For example, it takes less time for a processor to reference its local memory than to reference remote memory.

Reliability, Availability, and Serviceability (RAS)

The Altix 3700 Bx2 server series components have the following features to increase the reliability, availability, and serviceability (RAS) of the systems.

  • Power and cooling:

    • Power supplies are redundant and can be hot-swapped.

    • Bricks have overcurrent protection.

    • Fans are redundant and can be hot-swapped.

    • Fans run at multiple speeds in all bricks except the optional R-brick. Speed increases automatically when temperature increases or when a single fan fails.

  • System monitoring:

    • System controllers monitor the internal power and temperature of the bricks, and automatically shut down bricks to prevent overheating.

    • Memory, L2 cache, L3 cache, and all external bus transfers are protected by single-bit error correction and double-bit error detection (SECDED).

    • The NUMAlink interconnect network is protected by cyclic redundancy check (CRC).

    • The L1 primary cache is protected by parity.

    • Each brick has failure LEDs that indicate the failed part; LEDs are readable via the system controllers.

    • Systems support the optional Embedded Support Partner (ESP), a tool that monitors the system; when a condition occurs that may cause a failure, ESP notifies the appropriate SGI personnel.

    • Systems support remote console and maintenance activities.

  • Power-on and boot:

    • Automatic testing occurs after you power on the system. (These power-on self-tests or POSTs are also referred to as power-on diagnostics or PODs).

    • Processors and memory are automatically de-allocated when a self-test failure occurs.

    • Boot times are minimized.

  • Further RAS features:

    • Systems support partitioning.

    • Systems have a local field-replaceable unit (FRU) analyzer.

    • All system faults are logged in files.

    • Memory can be scrubbed when a single-bit error occurs.

System Components

The Altix 3700 Bx2 series system features the following major components:

  • 40U rack. This is a custom rack used for both the compute and I/O rack in the Altix 3700 Bx2 system. The power bays are mounted vertically on one side of the rack.

  • CR-brick. This contains the compute power, standard routers and DIMM memory for the Altix 3700 Bx2 series systems. The CR-brick is 4U high and contains four Super-Hub (SHUB) ASICs, eight Intel Intanium 2 processors, eight NUMAlink-4 router ports, and up to 48 memory DIMMs.

  • IX-brick. This 4U-high brick provides the boot I/O functions and 12 PCI-X slots.

  • PX-brick. This 4U-high brick provides 12 PCI-X slots on 6 buses for PCI expansion.

  • R-brick. This is a 2U-high, 8-port metarouter brick.

  • Power bay. The 3U-high power bay holds a maximum of six power supplies that convert 200-240 VAC to 48 VDC. The power bay has eight 48-VDC outputs.

  • D-brick2. This is a 3U-high disk storage enclosure that holds a maximum of 16 low-profile Fibre Channel disk drives.

  • TP900 disk storage module. This is a 2U-high disk storage enclosure that holds a maximum of eight low-profile Ultra320 SCSI disk drives.

  • SGIconsole. This is an optional combination of hardware and software that allows you to manage multiple SGI servers.

Figure 3-4 shows the Altix 3700 Bx2 system components.

Figure 3-4. Altix 3700 Bx2 System Components Example

Altix 3700 Bx2 
System Components Example

Bay (Unit) Numbering

Bays in the racks are numbered using standard units. A standard unit (SU) or unit (U) is equal to 1.75 inches (4.445 cm). Because bricks occupy multiple standard units, brick locations within a rack are identified by the bottom unit (U) in which the brick resides. For example, in a tall 40U rack, the CR-brick positioned in U05, U06, and U07 is identified as C05.

Rack Numbering

A rack is numbered with a three-digit number. Compute racks are numbered sequentially beginning with 001. A compute rack is a rack that contains CR-bricks. I/O racks are numbered sequentially and by the physical quadrant in which the I/O rack resides. In a single compute rack system, the rack number is always 001.

Optional System Components

The Altix 3700 Bx2 series system has the following external storage options:

  • Host bus adapter interfaces (HBA)

    • 2Gbit Fibre Channel, 200MB/s peak bandwidth

    • Ultra320 SCSI, 320 MB/s peak bandwidth

    • Gigabit Ethernet copper and optical

    • 10-Gigabit Ethernet PCI-X

  • JBOD (just a bunch of disks)

    • SGI TP900 Ultra320 SCSI

  • RAID

    • SGI TP9300, TP9300S, TP9500 or TP9500S, 2 Gbit Fibre Channel

    • D-brick2, 2 Gbit Fibre Channel

  • Data servers

    • SGI InfiniteStorage NAS 2000 Fileserver

    • SGI SAN Server 2000/San Gateway

  • Tape libraries

    • STK L20, L40, L80, L180, and L700

    • ADIC Scalar 100, Scalar 1000, Scalar 10000, and ADIC Scalar i2000

  • Tape drives

    • STK 9840B, 9940B, LTO, SDLT, and DLT

Availability of optional components for the SGI 3700 Bx2 systems may vary based on new product introductions or end-of-life components. Check with your SGI sales or support representative for the most current information on available product options.