Risk and reward
Building the new Symmetrix around a new architecture was a big risk for EMC. EMC Vice President, Chuck Hollis, says the company searched for two years for technologies to replace the old Symmetrix. In 2000, it committed to a matrix over switch architecture, setting EMC up for some hard times in 2002.

"We could have had a bus-switch based hybrid out a couple years ago," says Hollis. "We knew that 2002 would be a tough year in the high end. We knew that we'd be late in the market and that we'd have to play defense out there."

A May 2002 report from industry analyst AG Edwards warned that "EMC must aggressively increase the functionality, capacity and performance of its solutions to remain competitive." With the matrix architecture, EMC hopes to do exactly that.

The direct matrix architecture of the Symmetrix DMX (left) does away with intervening controllers like those in a crossbar-switch architecture to enable a host of direct, point-to-point connections between cache memory and the front-end and back-end controllers. The result is 64 GB/s of aggregate internal bandwidth--a quantum leap higher than the Symmetrix 8000's.

Here's the Cliff Notes: The matrix backplane provides a dedicated, physical link between each cache controller and every disk and front-end controller.

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Architecture comparison

The direct matrix architecture of the Symmetrix DMX (top) eliminates intervening controllers (such as those shown in the crossbar-switch architecture beneath) to enable a host of direct, point-to-point connections between cache memory and front- and back-end controllers. The result is 70.4GB/s of aggregate internal bandwidth that is higher than that provided by the Symmetrix 8000 family. A failed memory board takes down 16 of 128 total links, for a 12% bandwidth reduction. In a switched architecture the worst case is a failed crossbar switch, which darkens eight of 32 total links and yields a 25% bandwidth loss.

"When [data] comes in over a bus, you have to ask questions about where it's coming from and where it's going," says Hollis. "On the matrix it's all path to path. If it's on Wire 7, there is only one place where it can be coming from and one place where it can be going."

The hardwired interconnects help eliminate bus or switch controller latency and enable multiple parallel transfers that approach wire speed, says Hollis. This architecture enables controller intelligence to be distributed around a globally shared cache, an approach that until recently would have been too expensive.

"The concept of the matrix has only in the last few years been technologically feasible," says Passmore. "What EMC has done is move the electronics from the internal parts of the switch and move them out to the edge. The first question you have is: How in the world do I afford all those drivers and receivers? And the answer goes back to silicon design and components."

Assessing DMX
Published Symmetrix DMX benchmarks simulating a data warehouse workload may set high expectations among customers. According to EMC, a high-end Symmetrix DMX2000 array delivers 20,000 IOPS with a sustained response times of just over 3.5 ms. A comparable HDS Lightning 9980 V was benchmarked at about 6,000 IOPS with sustained response times just under 3.5 ms.

High-flying specs may grab headlines, but most IT managers are more interested in flexibility and cost questions. Symmetrix DMX offerings range from the low-end DMX800, which shares a modular cabinet design with EMC's midrange Clariion, to the Symmetrix DMX2000-P with 128GB global cache and 64 disk channels (see "Symmetrix DMX Model Offerings"). ESG Analyst Prigmore singles out the Symmetrix DMX800 as a potent offering that will offer performance and scalability on par with the Symmetrix 8830 while offering a lower entry price point.

"We expect to see the DMX800 go into places where Symmetrix has not been in the past," Prigmore says. "We see the DMX800 as having the most potential."

The DMX800 fills the space just above EMC's Clariion line, making enterprise-class business continuity features economical outside of large data centers. A company could deploy Symmetrix DMX800 units in regional offices, for example.

At the heart of the DMX family are the Symmetrix DMX1000 and DMX2000 products. The DMX1000 supports up to 144 disk drives, 48 front-end ports, 64GB of global cache memory and 18.4TB of usable capacity. The dual-cabinet DMX2000 doubles each of these specifications. EMC expects many DMX units to be configured for parity RAID operation, which protects data while maximizing disk utilization. Optimized RAID operations in the new DMX models help these systems approach the performance of mirrored configurations, but yield 75% more usable capacity.

While pricing was not available at press time, EMC says the list price for a DMX1000 with 12TB of usable capacity should run about one-third less than the price of high-performance Symmetrix 8830 sold last year. And who pays list these days for storage?

EMC plies the most demanding customers with the performance-minded DMX1000-P and DMX2000-P. These models share cabinet configurations with their non-P counterparts, but enable higher back-end bandwidth with double the number of drive channels. Where the DMX1000 and DMX2000 employ 16 and 32 2Gb Fibre Channel drive channels, respectively, the DMX1000-P and DMX2000-P are equipped with 32 and 64 back-end disk channels apiece. High-performance models will typically be configured with mirrored disks for maximum responsiveness. With disk mirroring, usable capacity maxes out at 10.5TB or 21TB, 43% less than on the non-P versions.

Unfortunately for mainframe users, Symmetrix DMX doesn't yet support FICON. The Symmetrix 8000 family has included FICON Fibre Channel ports for some time, but DMX models won't gain FICON capability until the third quarter of 2003. The delay poses an early challenge for the promising new architecture. Says Hollis: "This was the most important feature I wish was in the box at launch that wasn't."

ESCON, however, will be available for DMX at launch. EMC will install Symmetrix 8000 units for DMX customers until FICON-capable systems are available. For installed DMX units, the company will provide FICON daughtercards. Whether users will be willing to accept a delay remains to be seen.

This was first published in January 2003

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