You can tackle the CPU utilization problem a couple of ways. As always, there's the classic brute-force method: Servers with more horsepower have more CPU headroom and therefore are less affected by iSCSI. Simple, but expensive.
Our suggestion: Hardware, baby. Fibre Channel HBAs handle the FC protocol; likewise, to get the most out of your iSCSI-connected servers, you'll need a specialized adapter that will rein in CPU utilization.
These devices work in two ways. Some off-load the TCP stack onto hardware, relieving the system CPU of that burden. Adapters using this method are called TOE (TCP Offload Engine) cards, and they look like any other NIC to the operating system, though you have to add an external iSCSI initiator--the software drivers that make iSCSI work. Microsoft is slated to have one available next month.
The second method is similar in approach to the TOE card, but with a twist: iSCSI HBAs appear to the operating system to be SCSI cards, and they come with their own iSCSI initiators--in iSCSI parlance, the "iSCSI driver."
For our tests, we gathered iSCSI adapters from Adaptec, Alacritech and Intel Corp. in our Green Bay, Wis., Real-World Labs®. Invitations went to Emulex Corp. and QLogic Corp. as well, but iSCSI products from those companies were not ready in time for our test window.
We tested two iSCSI HBAs, the Adaptec iSCSI Adapter 7211C card and the Intel Pro/1000 T IP Storage Adapter, and one TOE card, the Alacritech 1001x1 Copper Single-Port Server and Storage Accelerator (we pity the advertising agency that has to come up with a catchy jingle for that).
Our test setup used a Cisco 9216 Fibre Channel switch with an iSCSI blade, a Nishan 3000 Series Storage Switch, a Cisco Catalyst 3550 Gigabit Ethernet switch, and a Eurologic SANbloc 2 Fibre Channel RAID enclosure with 14 73-GB drives. The cards were tested in three identical Dell 2650 2U servers with 1 GB of memory and two 2.6-GHz Pentium 4 processors.
Overall, we found these products a little raw. For example, many ease-of-use and convenience features are missing. Command-line implementations are common. But after talking with vendors, we believe that many of these early look-and-feel issues will soon be resolved. Moreover, even without management bells and whistles, iSCSI is not terribly hard to use.
Our individual results were interesting, to say the least. The Alacritech card performed well in every test--provided it had two targets (see "Multiple Target Woes"). But its overall CPU utilization was a bit higher than that of its rivals. The Adaptec card, meanwhile, didn't function as well in throughput or read tests, but it turned in a strong overall performance, with ry good CPU-utilization numbers. For its part, the Intel Pro/1000 T IP Storage Adapter did well in most tests and aced CPU utilization, but it has performance issues with reading, regardless of the number of targets.
The wild card was our NWC Custom test, which we designed to simulate real-world access patterns. The Adaptec iSCSI-7211C scored very well in this test and was simply the most consistent card in performance, posting CPU utilization scores that won outright or came very close in every test. Throw in a very competitive price (all pricing is MSRP) and you have an Editor's Choice award winner.
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