Storage Bottlenecks

Anyone who has followed the progress of PC and server architecture over the years knows that one part of the system always lags behind the others, creating a bottleneck. The bottleneck might lie in the processor speed's inability to fill the system bus. Then, when a new generation of processors comes along, the bottleneck might shift to the system bus. At the moment, the bottleneck for most servers is the inability of the system bus—typically, an aging PCI bus—to handle peripheral I/O. This bottleneck (which is at the heart of the Infiniband standard's development) is one reason that dense racks of thin servers are replacing multiprocessor systems. The problem is that a bridge controls access to server memory, and only one device can talk to main memory at a time.

Like general-purpose servers, storage servers suffer from limited client and server access to data stored on the disks that those servers control. That's one reason why Network Appliance's F840 Network Attached Storage (NAS) offering isn't that much faster than EMC's CLARiiON IP4700 NAS box. The current I/O technologies comprise a bottleneck. No matter how many NIC cards you shove into these machines, they still compete for the same system bus. In the near future, your LAN might run at 1.7Gbps (fibre channel) or 2Gbps (GigE), but your server throughput is still limited to 200Mbps.

Recently, when the 130-person startup company BlueArc briefed me about a new NAS offering, the SiliconServer, this throughput limitation came to mind. Geoff Barrall, one of BlueArc's founders and now its Chief Technology Officer (CTO), has explained BlueArc's technology to analysts, investors, and customers—and to me.

BlueArc has optimized and reduced the system bus into a set of custom application-specific integrated circuits (ASICs) that run at 2Gbps internally in a NAS head. The SiliconServer contains two internal system buses, each of which runs in one direction: one from users to storage and the other from storage to users (each at gigabit speeds).

At the heart of BlueArc's advance is eliminating the interaction of the data bus with software so that all of the data transfer occurs in hardware. Therefore, system upgrades are done on-the-fly and online. The result is that a SiliconServer runs at up to 10 times the speed of other NAS offerings. BlueArc is testing its product with streaming file applications such as video and audio transfers—where the speed would be an overwhelming technical advantage.

The large-frame vendors often cite NAS throughput problems when they sell Storage Area Network (SAN) solutions against NAS vendors. And throughput is one reason that customers tend to buy multiple NAS heads to service their file storage needs. One SiliconServer can replace several high-end NAS boxes. And BlueArc is pricing SiliconServer aggressively. The first version, the Si7500, a 2U server that can handle thousands of users at a time, is priced at less than $100,000 (similarly to a Network Appliance F840).

But throughput isn't the only technical advantage BlueArc has engineered into the SiliconServer. Another issue is NAS's lack of scalability. Because NAS doesn't scale, many companies install SANs instead of NAS—even though NAS is easier to deploy and offers good multi-OS support. The SiliconServer connects through a fibre channel to storage arrays that can—in a single rack—support up to 7TB using current disk technology. By connecting to external RAID controllers, the SiliconServer can support all RAID levels—and, even more significantly, can be scaled to up to 200TB. BlueArc expects to add clustering capabilities and perform remote replication by year's end, according to so Dr. Bryan Sweeley, vice president of BlueArc's Product Management and Marketing.

SiliconServer's speed and ability to scale to SAN-sized levels could dramatically change the landscape of enterprise storage deployment. Clearly, BlueArc has a breakthrough product—as a progression of analysts and others who've looked at this company's box have noted. Having looked at the Intel IOMeter's numbers myself, I agree with them. (IOMeter is Intel's software workload generator and measurement tool.)

Not all analysts agree, I should note, about how the product will fare against applications such as databases and messaging systems. In tests against 4KB (Microsoft Exchange) and 8KB READS (Microsoft SQL Server) the performance advantage of 30 Dell 1U servers loading against the BlueArc fell to 5 to 6 times the speed of its competitors. It wasn't clear from those tests whether a problem occurred in filling the SiliconServer's I/O pipe—or the server hit a real limitation.

In any case, a great product doesn't always translate into long-term success. BlueArc is the right product at the right time in the right place. The company has an 18-month to 2-year advantage over the field—during which gigabit-speed networking products will drive this market forward. But other vendors can catch up if people don't learn about the SiliconServer quickly enough. Additionally, the software BlueArc offers, although functional, isn't as mature as its hardware. Still, if you're considering a SAN or NAS offering from a competitor, you should take a look at BlueArc, one of the most significant products I've seen lately.