Bring on the 2G sometime soon....
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F E A T U R E
QLogic Makes Sense of Fibre Channel
October 1, 2001
By Steven J. Schuchart Jr.
When we got our hands on some 2-Gb Fibre Channel devices, we were really excited. After all, this is cutting-edge technology, so new that the paint was still tacky on some of the equipment we received. A few months later, we've come to a painful conclusion: Wrapping your hands around a cutting edge buys you a trip to the hospital for stitches. We took the pain so you won't have to.
Once you've built a SAN (storage area network), you need to optimize performance. Your main focus here should be on three things: speed, reliability and interoperability. Users want their data yesterday, and applications such as streaming video and high-performance CAD/CAE applications need fat pipes. Although challengers, such as 10 Gigabit Ethernet and serial ATA (Advanced Technology Attachment), promise big bandwidth, Fibre Channel has proved it can deliver. Still, the threat posed by 10 Gigabit Ethernet looms large over the Fibre Channel world. Familiar terminology, familiar companies and legions of people who know Ethernet mean that, once it comes to fruition, 10 Gigabit Ethernet could crush the Fibre Channel market. But that's another article.
Here are our other conclusions: The Fibre Channel community has come a long way in interdevice compatibility, but some bugs still need to be worked out. Plug-fests and testing can go only so far. Companies need to have every brand HBA (host bus adapter), switch and JBOD (just a bunch of disks) on hand to make interoperability a reality. Equipment swaps and loans among vendors -- and just a little bit more trust in the Fibre Channel community -- will do wonders to get this done.
The road to testing our 2-Gb Fibre Channel HBAs was rocky, but in the end, it was worth the pain. Fibre Channel is undoubtedly fast; however, it's also complex. The standards movement for Fibre Channel began in 1988 and Fibre Channel probably has the largest and most intricate set of standards documents of any protocol. Given the level of sophistication, we weren't surprised at the incompatibilities that plagued us.
Basics
There are three basic Fibre Channel topologies: point to point, arbitrated loop and fabric. All versions of Fibre Channel offer a long data path (Fibre Channel has a maximum distance of 10 kilometers on multimode optical fiber), which provides tremendous flexibility for your data center and nearby locations. Point to point is a simple setup in which the transmit ports are connected to the receive ports on a pair of devices. Arbitrated loop, which is by far the most common, is when you have multiple devices connected in a daisy-chain fashion without a switch. An arbitrated-loop device will send out its ALPA (arbitrated loop physical address). If that address completes the loop and comes back to the originating device, that device has control of the loop and may transmit data to a destination device. (You'll find more on specific terms in "Any F_port in a Storm".)
In fabric mode, two devices communicate without a direct connection -- in other words, they are connected to a switch. Each Fibre Channel frame can take a different path to the destination device; the frames need not arrive in order. The switched fabric topology lets you connect multiple data paths to your storage and servers, boosting reliability (see "Switched Fabric Network"). This setup can bring your network to five nines of uptime -- if any one path for the data is cut, the data finds its way around.
Another advantage of a fabric is that you can connect older 1-Gb Fibre Channel devices and new 2-Gb devices without dropping the newer devices to 1 Gb. This provides real flexibility.
In addition, the new 2-Gb Fibre Channel devices connect with a new type of connector and optical fiber cable, called Duplex LC. Also, SFP (small form-factor pluggable) GBICs (gigabit interface converters) have increased the density of Fibre Channel switches. Standard GBICs are 1.5 inches wide, while SFP GBICs are only 0.65 inches. The only drawback is that SFP GBICs are fragile and hell to work with, and the Duplex LC connectors on the cable are fragile as well.
While we're sure they will work just fine once in operation, initial setup is a real chore. We had GBICs from PicoLight and the venerable Finisar Corp. The PicoLight units have little pull tabs to remove them from the switch or HBA. However, these tabs fall off when the little metal RF shields fall off. The Finisar SFP GBICs have little buttons to push to get them out of the devices. Neat idea, but the buttons rarely work, and some switches are not suited to this kind of removal. When you are going to play with SFP GBICs, make sure you have extras -- and have your Leatherman multitool handy as well.
Switched Fabric Network
Click here to enlarge
The Meat
We tested 2-Gb Fibre Channel HBAs from Adaptec, Atto Technology, Emulex Corp. and QLogic Corp. We also invited JNI Corp. to participate, but the company declined because its Microsoft Windows drivers were not yet available.
These adapters offer different features, software and performance levels. To avoid compatibility problems, we got in three switches: Gadzoox Networks' SlingShot 4218, QLogic's SANbox 2 and Vixel Corp.'s 9000 Series 2. After some gyrations, we decided to use the Vixel switch for our tests. The other switches performed great, but we eliminated the QLogic in fairness to the other HBA vendors, and we were not able to keep the Gadzoox long enough to complete our testing. Because the Vixel switch was causing some performance issues with the Emulex card, we decided to test Emulex's entry separately. We felt this was the fair thing to do (see "Emulex Earns Extra Credits").
Looking at our performance results (see table below), you will see that some adapters, particularly the Atto ExpressPCI 3300 and the QLogic QLA2300F, have very similar numbers -- essentially, they tied. But bear in mind that you need to pay attention to more than maximum throughput numbers. CPU utilization, read total bytes versus write total bytes, total bytes read and written all paint a picture of HBA performance. Just as with a car, it's not all about top-end speed, but also gas mileage and handling.
When you purchase Fibre Channel equipment, you need to make sure that it is going to interoperate. In our tests, "plays well with others" was not always a reality. Press your provider for a demonstration or some guarantee that its equipment is going to function as advertised. Right now there's a lot of "Sure, our switch works with that HBA and that JBOD." The reality is that, though standards are well defined, compatibility is a very new thing for the Fibre Channel community. There have been leaps and bounds made on this front, but the devil is in the details.
QLogic Makes Sense of Fibre Channel
QLogic Corp. QLA2300F
Performance Test Results
QLogic's adapter performed without much tweaking on all the hardware we had in for testing. This, combined with error-free operation, earned it our Editor's Choice award.< The performance numbers from this PCI card, especially its CPU utilization stats, are impressive, and we found it to be the easiest and most trouble-free card we tested. Setup was easy, and driver installation a snap. This card is also one of the fastest we tested, with one of the lowest CPU utilization rates.
Two quibbles: The QLA2300F came with a CD, titled the QLogic Management Suite, that was supposed to include a utility on it called Qlview for Fibre Channel. However, after extensive searching, we could not find the utility. There were applications for the SCSI HBAs, but none for the Fibre Channel cards. This CD could benefit from an autostart file and a menu. Also, the QLA2300F does not support the MD2 low-profile PCI 2.2 standard.
The QLA2300F's BIOS is complete. You can manage more than one board and get at all the advanced settings you might need in case of trouble. In our maximum throughput testing, the QLA2300F tied, within a 3 percent margin of error, the Atto ExpressPCI 3300 (no surprise since the ExpressPCI uses the same QLogic silicon as the QLA2300F).
However, the QLogic card's superior CPU utilization pushed it over the top. In the maximum I/O operations per second test, the QLA2300F again tied with the Atto card and again took the crown with superior CPU utilization. On the database test, it scores well but does not win. In the final contest, the Web server test, the QLA2300F ties with the Atto on performance but prevails again thanks to its superior CPU utilization stats. Clearly, QLogic has itself a winner, a consistent, stable card that can deliver the numbers.
QLA2300F, $1,995 with a standard three-year warranty. Available: Now. QLogic Corp., (800) 662-4471, (949) 389-6000; fax (949) 389-6126
Nice to know that Q not only has the best priced HBAs, but also the best HBAs. ANd remember that the runner up is also based on QLGC silicon. Way to go Q! Now if we could read some Switch reviews like this one on HBAs! |
