iSCSI is the user favorite for block-based Ethernet storage. But there are two competing Ethernet protocols--ATA...
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over Ethernet (AoE) and Storage over IP (SoIP)--that may be able to gather enough momentum with home and small business users to overtake iSCSI in the enterprise.
AoE and SoIP offer higher speeds without the performance overhead associated with TCP. AoE doesn't use IP at all, but rather the native Ethernet protocol, thus avoiding IP overhead. SoIP works with the User Datagram Protocol (UDP); it gives users the flexibility to assign an IP address to individual storage targets so UDP can communicate with multiple targets concurrently and stripe data across multiple disks for better performance.
"Unlike TCP, which puts data in order, UDP can use two additional IP commands--broadcast and multicast," says Ryan Malone, senior director of marketing at Zetera, Irvine, CA. "This allows us to take advantage of UDP's ability to talk to a bunch of IP addresses at the same time."
Zetera and Coraid have taken different approaches to gain traction for SoIP and AoE, respectively. Zetera bundles its proprietary SoIP with storage products like Netgear's Storage Central SC101 and Hammer Storage's Z-Box. "Zetera technology has already shipped in over 100,000 units, the majority of which are Netgear SC101s," says Malone, "which Netgear considers one of its most successful product launches."
Coraid has opted for an open-source strategy. Operating system drivers for the AoE storage protocol are included with the main Linux kernel beginning with Linux Version 2.6.11, and open-source drivers for FreeBSD and Solaris are available in beta for download at SourceForge.net. AoE drivers for Microsoft Windows, however, are only available from Rocket Division Software in Kyiv, Ukraine (for $95).
Brantley Coile, Coraid's CTO, sees protocols like SoIP and iSCSI as problematic. "iSCSI was designed to run on a huge box with a huge controller, while SoIP is closed and proprietary," says Coile. "The people AoE [is] trying to help cannot afford or are not comfortable with those approaches."
Putting aside performance benefits, these protocols do have their drawbacks. Neither AoE nor UDP natively guarantee packet delivery; to prevent packet loss, users must deploy each vendor's respective drivers on the host and storage arrays for packet checking. To deliver this in SoIP, says Zetera's Malone, "Zetera built a Fibre Channel-like acknowledge system on top of UDP to ensure the reliable delivery of data."
Enterprises will likely balk at the use of proprietary software to perform tasks already done by the TCP/IP protocol. EqualLogic, a provider of iSCSI storage arrays, questions the use of proprietary protocols and drivers. "Our enterprise customers want native operating system drivers and do not want to install vendor-specific drivers on their OS, especially ones that are unsigned or unblessed by vendors like Microsoft," says Eric Schott, EqualLogic's director of product management.
Another question is whether the performance improvement provided by AoE and SoIP is enough to justify using them instead of iSCSI. "iSCSI is freely available, and home and small business users are typically not sensitive to performance, so what problems do these protocols solve?" wonders Schott.
But perhaps the biggest challenge AoE and SoIP face is the lack of broad storage product support. Only Netgear and Hammer Storage offer products that support SoIP, and Coraid is the only provider of storage devices that support the AoE protocol. Still, says Coile, "we have over 500 customers, and we are seeing many of them moving from trying it to expanding it."
--Jerome M. Wendt