EMC DMX 3 ArchitectureToday we will discuss about DMX 3 architecture in detail.The DMX-3 fully leverages the EMC industry-leading storage.The Symmetrix DMX-3 is incrementally scalable, supporting from 96 to 1,920 2 Gb/s high-performance Fibre Channel disk drives, providing a maximum raw capacity of approximately 1 PB.(In special setup we can configure maximum 2400 disks in DMX 3 models).

As the name indicates, DMX works on a direct matrix architecture. That means there will be direct connect connectivity between the front end directors, global memory and backend directors. Direct Matrix Architecture (DMX) supports up to 128 point-to-point serial connections within the DMX system. In the Direct Matrix Architecture, contention is minimized because control information and commands are transferred across a separateand dedicated message matrix. The major components of Symmetrix DMX architecture are the front-end channel directors (and their interface adapters), global memory directors, and back-end disk directors (and their interface adapters). The matrix midplane provides configuration flexibility through the slot configuration. Each director slot port is hard-wiredpoint-to-point to one port on each global memory director board. We will check each parts in detail in the later part of this post.DMX 3 Block DiagramIn a fully configured Symmetrix DMX-3, each of the eight director ports on the sixteen directors connects to one of the 16 memory ports on each of the eight global memory directors. These 128 individual point-to-point connections facilitate up to 128 concurrent global memory operations in the system. Below picture illustrates the point-to-point architecture and the interconnection of the major components of the Symmetrix DMX-3 systems.

The Symmetrix DMX-3 is composed of a system bay and one to eight storage bays.Symmetrix DMX-3 system bay:Below picture will give an idea about DMX 3s system bay components. It is showing the front and rear view of system bay

Cooling fan modules:Three 3-fan modules maintain air circulation and cool the unit internally.Card cage and midplane:The midplane acts as the backborn of DMX 3. This is the hardware which will interconnect the directors with its corresponding adapters.It has front end and backend slots.The front 24 slots contain global memory directors, disk directors, and channel directors (front-end Fibre Channel, ESCON, FICON, and iSCSI channel directors a, or GigE Remote directors). The rear slots contain the channel host adapters, GigE Remote adapters, disk adapters, and the Communications and Environmental Control Modules (XCMs).Below figure will give idea about front end midplane slot configuration.

On the rear side of the midplane as shown below, the adaptersreside behind their respective directors, and two slots behind thememory are reserved for the XCM pair.

Front-end Modules:The front end modules consist ofChannel directors/adapters which will give access to hosts to the storage system and remote director adapters which are used for remote replications(SRDF).Up to 12 channel directors connect to the front side of the midplane and the adapters to the rearside of the midplane in the system cabinet.Back-End Modules:Backend modules consists of disk directors and adapters.Two, four, six or eight disk directors connect to the midplane in the front of the cabinet. Each diskdirectors adapter provides the interface to the Fibre Channel disk drives. The adapter connects to the opposite side of the midplane in the rear of the cabinet.Global memory directors:The Symmetrix DMX-3 global memory director technology is one of the most crucial components of a Symmetrix system. The DMX-3 uses global memory directors that use industry-standard Double Data Rate Synchronous Dynamic Random-Access Memory (DDR SDRAM), the latest generation of DDR SDRAM chip technology. All read and write operations transfer data to or from global memory. Any transfers between the host processor, channel directors, and global memory directors are achieved at much greater electronic speeds than transfers involving disks.Two, four, six, or eight global memory directors provide up to 512 GB (256 GB effective) total global memory, available in 8 GB, 16 GB, 32 GB, and 64 GB global memory director capacities.The DMX-3 global memorydirectors work in pairs. The hardware writes to the primary globalmemory director first, and then automatically writes data to thesecondary global memory director. All reads are from the primarymemory director. Upon a primary or secondary global memorydirector failure, all directors drop the failed global memory directorand switch to a nondual write mode. Striping between globalmemory directors is default.

Each global memory director has 16 ports with point-to-point serialconnections between the global memory director and channel or diskdirectors (16 directors) through the direct matrix. Each memorydirector port consists of a pair of full-duplex serial linkstwo seriallinks out (TX) and two serial links in (RX).Each of the eight director ports on the 16 directors connect to one ofthe 16 memory ports on each of the eight global memory directors(as shown in below picture). These 128 individual point-to-pointconnections facilitate up to 128 concurrent cache operations in thesystem.Communications and environmental control module (XCM):In older DMX models, we were using two different hardware for communication (Communication Control Module CCM) and for environmental monitoring (EnvironmentalControl Module ECM). In DMX3 these two hardware functions are combined together and made a single hardware called XCM. Two communication module and environmental control modules (XCMs) connect to the midplane in therear card cage.The XCMs primary function is to act as a communications agentbetween the service processor (KVM and server) and the embeddedprocessing nodes within the system.It hasEthernet interface between the directors (channel, disk, and memory) and the service processor.The XCM monitors and logs environmental events across all criticalcomponents and reports any operationalproblems. Critical components include channel and disk directors,global memory directors, power supplies, power line input modules,fans, and various on/off switches. The XCM environmental control iscapable of monitoring each components local voltages ensuringoptimum power delivery. Temperature of directors and memory arealso continuously monitored. The AC power main is checked for: AC failures Transfer to auxiliary DC failures Current sharing between DC supplies DC output voltage Specific notification of overvoltage conditionIt also has connectors for paths between the XCM and the BBU modules (in the system bay and the storage bays) for sending commands and receiving status.Power supplies:The system bay contains up to eight power supplies that are split intotwo power zonesPower Zone A and Power Zone B, consisting ofup to four power supplies each.One zone can maintain power for the entire system bay independent of the power supplies in the other zone. The DMX-3 is available in three-phase Delta or three-phase WYE configurations.Power distribution panel (PDP), power distribution unit (PDU), and AC connectors:Two PDPs, one for each zone, provide a centralized cabinet interface and distribution control of the AC power input lines when connected to the system bay PDUs. The PDPs contain the manual On/Off power switches, which are accessible through the rear door. The PDUs, one for each power zone, provide the main interface between the input AC from the PDPs and the various components contained within the system bay.Battery backup unit (BBU) assembly consisting of two BBU modules:Up to eight BBU modules provide backup for each of the power supplies. If AC power fails, the BBU modules can maintain power for two 5-minute periods of AC loss while the Symmetrix system shuts down.Service processor (keyboard, video display, and mouse KVM), server, and uninterruptible owersupply (UPS):The service processor consists of a KVM and a server that connects to the Symmetrix subsystem through an Ethernet interface. The service processor uses an external modem for communicating with the EMC Customer Support Center when the Symmetrix system detects an error condition. The service processorautomatically dials the Customer Support Center whenever theSymmetrix system detects a component failure or environmentalviolation. An EMC Product Support Engineer at the CustomerSupport Center can also run diagnostics remotely through the serviceprocessor to determine the source of a problem and potentiallyresolve it before the problem becomes criticalThe service processor is used to download the Symmetrix system configuration to the directors and provides diagnostic and maintenance utilities for the Symmetrix system. The server battery backup is provided by a UPS.Storage bays hardware Components:Below picture will give an idea about Storage bay

Drive enclosures:The Symmetrix DMX-3 storage bay is configured with capacities of 120 or 240 disk drives. Eachdrive enclosure includes the following components: Redundant power and cooling modules for disk drives Two Link Control Cards (LCC) From 4 to 15 Fibre Channel disk drives per drive enclosureThe storage bays can be populated with any combination of DMX disk drives (73 GB, 146 GB, and300 GB 10,000 rpm drives; 73 GB, 146 GB, and 300 GB 15,000 rpm drives; and 500 GB 7,200rpm drives) Some configuration restrictions may apply.Battery backup unit (BBU)modules:Two BBU modules are required for four drive enclosures (up to eight BBU modules support up to16 drive enclosures in one storage bay). The BBU modules provide backup power to the driveenclosures.Power distribution panel (PDP),Power distribution unit (PDU),and AC connectors:Two PDPs, one for each zone, provide a centralized cabinet interface and distribution control of theAC power input lines when connected to the storage bay PDUs. The PDPs contain the manualOn/Off power switches, which are accessible through the rear door. The PDUs, one for eachpower zone, provide the main interface between the input AC from the PDPs and the BBUmodules to the drive enclosures contained within the storage bay.Hope this was helpful for you.I will be publishing a post about DMX 4 in future.keep visiting EMC SAN Info.If you have any doubts,questions,do comment below or use our Ask Question section.

Difference between EMC DMX 3 and DMX 4EMC DMX 3 and DMX 4 are EMCs two well-known EMC SAN storage products. DMX 4 is the last model in direct matrix architecture series, after that EMC introduced their virtual matrix interface model EMC Vmax. Today we will discuss about the basic difference between EMC DMX 3 and DMX 4.Almost all the features are same in both DMX 3 and DMX 4 models. We can say like DMX4 is the version two of DMX3.So lets check the basic difference between EMC DMX 3 and DMX 4There are 2 major differences between these models.In DMX 3 the drives are connected to the Link Control Card(LCC) through a traditional arbitrated loop where as in DMX 4 models,drives to LCC connection is point to point.In DMX 3 maximum backend channel speed is 2Gb/s and same in DMX 4 is 4Gb/sTraditional arbitrated loop v/s point to point loop:Below picture shows the traditional loop concept.

Here all the drives are connected to the LCC through a traditional arbitrated loop. If you want to write any data to the drive 4,the data has to pass through the drives 1,2 and 3 from LCC. Due to loop functionality, signal integrity and protocol issue at a drive will propagate to other drives in the loop.Below picture shows the point to point connectivity

In DMX 4 models, we have CTS ( Cut Through Switch ) point to point connections between LCC and drives. Like normal traditional loop in DMX 3, data does not have to pass through all its preceding drives to reach destination. This point to point connection help us to detect and isolate a faulty component like Drives,Cables,LCC very easily.This cut through switch connectivity enables port monitoring capability to each drive port, allowing for better fault detection and isolation. Performance increases since the data does not have to be passed through every drive in the loop. Point-to-point connections between LCC and drives gives DMX 4 models a significant gain in signal integrity compared with DMX 3 disk enclosures. As can be seen in above picture, the physical layout of LCCs provide shorter connections to each drive.Backend drive loop Speed:As I told earlier other difference between DMX 3 and DMX 4 is the backend drive loop speed. The maximum backend speed in DMX 3 is 2Gb/s and in DMX 4,it is 4Gb/S. DMX 4 can work on 2Gb/s as well.Comparison between EMC DMX 3 and DMX 4Features/SpecificationSymmetrix DMX-3Symmetrix DMX-4

Open systems/mainframeOpen systems and MainframeOpen systems and Mainframe

CPU Processors1.3 GHz PowerPC1.3 GHz PowerPC

Memory Directors88

Maximum Global Memory512 GB (256 GB effective)512 GB (256 GB effective)

Fibre Channel Back-endTraditional LoopPoint-to-Point

Maximum Back-end Channel Speed2Gb/s4Gb/s

Disk adapters1, 2, 3, or 4 DA pairs1, 2, 3, or 4 DA pairs

Disk Ports16-6416-64

Number of disks96-240096-2400

Maximum raw capacity (TB)1103.131103.13

Usable Connectivity Ports2-64x Fibre Channel host/SAN ports2-8x Fibre Channel remote replicationports2-48x iSCSI ports2-48x FICON host ports2-8x GigE remote replication ports2-64x ESCON host ports2-8x ESCON remote replication ports2-64x Fibre Channel host/SAN ports2-8x Fibre Channel remote replication ports2-48x iSCSI ports2-48xFICON host ports2-8x GigE remote replication ports2-64x ESCON host ports2-8x ESCON remote replication ports