One of the benefits that networked storage solutions confer is a significant reduction in the number of servers in your network through the consolidation of file and application data onto a smaller number of Network Attached Storage (NAS) and Storage Area Network (SAN) devices. As I study the consolidation trend, I'm seeing impressive numbers--server reduction ratios in some cases as high as 10 to 1. One result of this reduction is that more data--specifically, an increase in the number of TCP/IP packets--must be jammed through a smaller number of pipes. Although Fibre Channel SAN devices aren't affected by TCP/IP traffic, the CPUs of NAS or iSCSI-based SAN devices are.
The TCP/IP protocol was designed to send data packets over great distances across unreliable connections. Because of the unpredictability of public networks, TCP/IP performs a lot of error correction handling to ensure that packets move safely and accurately from source to destination. This error handling delivers a performance hit to storage devices' CPUs. To address the problem, several vendors have developed TCP/IP offload engines (TOEs)--essentially add-on chips to NICs that fit inside existing NAS and iSCSI SAN devices. By offloading the TCP/IP overhead from the CPU, TOE cards can increase the throughput of a NAS or iSCSI SAN device.
Most iSCSI SAN solutions include TOE cards to guarantee the performance necessary to any enterprise setting. iSCSI, which uses the TCP/IP protocol, has a TCP/IP overhead that Fibre Channel solutions don't have. Because TOE cards reduce this overhead, they are typically included in iSCSI SAN solutions.
One vendor, Alacritech ( http://www.alacritech.com ), supplies TOE cards to NAS vendors, including Hewlett-Packard (HP), IBM, Sony, Pinnacle Systems, and Iomega. HP claims that adding Alacritech TOE cards to its NAS solutions increases system performance as much as 30 percent or more. Iomega recently introduced two high-end NAS products to its portfolio and includes Alacritech TOE cards with each solution. Iomega claims the TOE cards bring about an increase in performance as high as 20 percent. In addition to Alacritech, vendors Adaptec ( http://www.adaptec.com ), Intel ( http://www.intel.com ) and Xiran ( http://www.xiran.com ) produce TOE cards. Xiran's partners include Sun Microsystems and RealNetworks, and Xiran emphasizes solutions for multimedia content delivery over TCP/IP.
Here's the bottom line. If you're looking for a mid- to high-end SAN solution, make sure it either comes with a TOE card or will let you add a card later. The ability to nail down an extra 20 percent to 40 percent in performance speed is a trick you'll want up your sleeve. Don't even bother with potential iSCSI SAN solutions unless a TOE card is included in the box. Getting a TOE in your networked storage solution can increase performance and possibly save you from a costly network upgrade or the purchase of additional storage devices.