What the Heck Is HyperSCSI?

'Raw Ethernet' SAN protocol isn't bogged down by TCP/IP - but almost no one's heard of it

September 26, 2003

4 Min Read
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Data transport protocol iSCSI may have begun gaining industry recognition as a low-cost alternative to Fibre Channel in storage networks -- if not exactly traction just yet -- but its not the only candidate sitting in the hallway (see Microsoft Sparks iSCSI Liftoff and iSCSI Gets Go-Ahead). Another transport protocol, HyperSCSI, is also angling for the position of providing inexpensive, Ethernet-based SANs to the masses.

The HyperSCSI protocol, originally developed by researchers at Singapore's Data Storage Institute (DSI) in 2000, is designed for transmitting Small Computer System Interface (SCSI) data and commands across raw Ethernet, allowing companies to connect to and use remote SCSI and SCSI-based devices over a network as if it were directly attached locally. The DSI is a joint venture of Singapore's Agency for Science, Technology, and Research (A*STAR) and the National University of Singapore (NUS).

By contrast, iSCSI -- developed under the auspices of the Internet Engineering Task Force (IETF) -- sends SCSI commands over TCP/IP.

HyperSCSI's supporters claim that it not only dramatically slashes the price of SAN connectivity compared with both Fibre Channel and iSCSI, but also that it offers far better performance than its IP-based cousin.

By sending data blocks across raw Ethernet, the protocol completely eliminates the TCP/IP overhead that slows down iSCSI, according to HyperSCSI's supporters. In fact, the protocol's developers claim, it can match Fibre Channel performance with only a 21 percent increase in CPU utilization and 3.4 times more IRQs (Interrupt Requests, which are used to signal to a CPU that a peripheral event has started or terminated). Meanwhile, they claim that iSCSI chews up 33 percent more CPU utilization and 6 times more IRQs to match Fibre Channel's performance.“It’s a pretty interesting approach,” says Graham Smith, senior I/O planning manager in Hewlett-Packard Co.'s (NYSE: HPQ) Enterprise Unix Division. “It really gets around the problem of offloading TCP/IP.” Smith adds, however, that HP doesn't currently have any plans to support HyperSCSI in any of its products.

And that’s not all. Since HyperSCSI was released as open-source software last year, it’s free and licensed under the GNU General Public License (GPL). “It’s not only free as in beer, but also free as in speech,” says Jesse Keating, systems engineer with Linux desktop vendor Pogo Linux who has experimented with HyperSCSI. “So if you need to make alterations, the code is available... You don’t have to rely on the 'governing bodies' of HyperSCSI to do it.”

With all these advantages, you might expect everyone in the industry to be looking at the new protocol. Instead, the response many people have to questions on the subject is: “HyperWHAT?”

While many industry vendors have been talking about iSCSI for the past couple years, HP’s Smith says it’s hard to say how seriously to take the HyperSCSI push, since it’s mainly only being talked about at the Data Storage Institute. “It looks a little like just another university project,” he says, but allows that, “of course, a lot of good technologies came through that channel.”

In addition to obscurity, HyperSCSI is, of course, also suffering from its share of technological concerns. While putting SCSI on raw Ethernet may speed up performance, there are also disadvantages associated with skirting TCP/IP, Smith says. “Without TCP/IP, it has no real error-recovery mechanism or guarantee that packets get delivered. It also appears to be quite limited in scaleability.”Other industry players aren’t quite so discreet. “I would describe it as a beer can with a motor,” says Andre Hedrick, president and CTO of iSCSI software vendor PyX Technologies Inc. [Ed. note: I need a beer!] “It will go really fast, but just hope there’s not a problem, because there’s nothing there to protect you.” He insists that if you turned off the internal payload checks on iSCSI, it would scream down the wire, too.

In addition, Hedrick points out, HyperSCSI isn’t based on industry standards. “This is great for folks that want to be locked into a single vendor without any path to get out,” he wrily notes. Moreover, the only HyperSCSI implementation available today is for Linux.

While there are plenty of pros and cons to the raw Ethernet-based HyperSCSI protocol, Balint Fleischer, CTO at Sun Microsystems Inc. (Nasdaq: SUNW) says it’s irrelevant, since customers aren’t asking for the technology.

“We’re not negative or positive,” he says. “We just haven’t seen it popping up on our radar screen.”

— Eugénie Larson, Senior Editor, Byte and Switch

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