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Understanding Fibre Channel Technology
 

 

Choosing the correct Fibre Channel Host Bus Adaptor

ATTO TECHNOLOGIES | ANTARES | BROCADE | CROSSROADS | EMULEX | GADZOOX

JNI | QLOGIC | VIXEL

Full line of new, used and refurbished Fibre Channel HBA's, drives, and RAID solutions

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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

 


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'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.

Atto was an interesting addition to our test as the company is using the QLogic ISP2300 chip as the engine for its board. Don't rush to judgment, however -- the company has its own clean board design and its own BIOS and drivers. The performance of this card was very good, in some cases better than that of the QLogic board, but the CPU utilization was high on some of our tests.

When we installed the ExpressPCI 3300, our Microsoft Windows 2000 Server installation started to crash during the boot process. We were puzzled by this behavior because, to avoid contamination, each HBA has its own copy of Windows 2000 Server. After a few frustrating minutes we called Atto support and found out that its adapter is set to BIOS boot mode at the factory, and the crashes were caused because the ExpressPCI 3300 and the internal Compaq Computer Corp. SCSI RAID controller in our server tried to occupy the same space at the same time. With that little problem solved, we proceeded to boot the system up and load the drivers.

Everything went fine, and the ExpressPCI 3300 put up some nice performance numbers, losing out to the QLA2300F only in the CPU utilization category. In fact, the ExpressPCI exhibited the highest CPU usage of any card on every category except for the maximum throughput test, where the Adaptec 9210LP had the higher utilization.

Like the QLogic QLA2300F, Atto's card does not support use in MD2 form factor machines, but with the amount of open space on Atto's clean design, that may come in the future.

The Adaptec 9210LP is noteworthy in that Adaptec partnered with Agilent Technologies for this card, which even has Adaptec/Agilent Technologies silk-screened on the top. The 9210LP uses Agilent's new Tachyon XL2 chipset and is the smallest card in the review. The 9210LP also comes with interchangeable faceplates for installation in servers that require MD2 form factor or standard card slots, and Adaptec's boot-time BIOS screen can be accessed in the same manner as its omnipresent SCSI cards: ctrl-A when prompted.

We had some issues with the 9210LP, however. In our first round of testing it scored only 101.49 MB per second on the maximum throughput test. Puzzled, we rechecked our switch configuration. Everything was set at the full 2 Gb (200 MB) per second rate. The 9210LP was logging into the switch as a 2-Gbps device. We called Adaptec tech support to see what the problem was, and it turns out that the current versions of Adaptec's drivers are having difficulty reading a registry key to set the adapter to N_port mode. Adaptec provided us with a fix, which forced the card into N_port mode operation for reliable performance measurement. Running the card under N_port, we were able to achieve 195.30 MB per second, a considerable increase and what we would expect. The updated driver will be available on Adaptec's Web site by the time you read this, according to company officials.

In the other tests, the Adaptec 9210LP came up short -- extremely so in some cases. The results in our two real-world simulation tests -- database server and Web server -- were particularly dismal. In these tests the 9210LP moved far less data than did the other cards and at a slower rate.

There are also a couple of other issues with this card. First, it lacks the ability to boot through a fabric network. This is a serious shortcoming, as all the other HBAs in this review have that ability. Another thing we noticed was that there is a feature in the 9210LP's BIOS to scan the devices connected to the HBA and show them on screen, similar to what the company's SCSI HBAs do. This feature does not work when connected to a switch. It works only in arbitrated loop mode. Not a huge problem, but when we were first hooking this HBA up, we assumed that this feature worked and that we had a connection problem to the JBODs. If this feature worked it would give all kinds of information on the devices connected to the HBA, such as device number, ALPA and Fibre Channel World Wide Name.

The BIOS settings on this card are also particularly sparse. The only settings we could change were the boot BIOS support, Fibre Channel hard ALPA, device scanning order and host adapter speed. While we don't like to monkey with base settings if we can avoid it, we do like to be given the option. Although we think this will be a good card after Adaptec and Agilent work out the bugs with performance and add all the features that the other cards offer, we cannot recommend it in its current incarnation. When asked, Adaptec was vague on when an updated version will be released.

Fibre Channel HBAs

No one wants to be the first to adopt new software or a new technology. "Let someone else find the bugs," we say. Sometimes, though, a bleeding-edge technology is too tempting to ignore. That's how we felt about the new crop of 2-Gb Fibre Channel HBAs (host bus adapters), which promise to double the speed of Fibre Channel connections. So we set out to test HBAs from Adaptec, Atto Technology, Emulex Corp. and QLogic Corp. at our Green Bay, Wis., Real-World Labs®. Considering the morass of Fibre Channel standards documents and the sketchy nature of vendor interoperability, we expected some rough going, and we weren't disappointed. In the end, this lack of interoperability forced us to look at Emulex's HBA individually (see "Emulex Earns Extra Credits"). Among the three cards left in our comparative review, QLogic's QLA2300F took our Editor's Choice award thanks to its ease of setup, error-free operation and superior performance numbers. In the end, we were glad we'd stuck with our tests, despite the pain. But next time we may just let someone else take the hits first. ... Nah.

We tested our Fibre Channel switches using Intel's IOMeter and running a suite of four tests. In our maximum throughput test, we looked at the maximum rate at which an HBA, coupled with a switch and a JBOD array, would run. The second test simulated database performance. The third was a maximum I/O rate test to see how many I/O operations per second each HBA could handle. And the fourth test, a Web server test, simulated the load a typical Web server puts on a storage network. The list below shows the setup of IOMeter for each test.

Maximum throughput test: Transfer request sizes set to 64 KB; percent read/write distribution, to 100 percent read; and percent random/sequential distribution, to 100 percent sequential.

Database test: 2 KB random I/Os with a mix of 67 percent reads and 33 percent writes, representing a typical database workload.

Maximum I/O rate test: Transfer request size set to 512 bytes; percent read/write distribution, to 100 percent read; and percent random/sequential distribution, to 100 percent sequential.

Web server test: Change the transfer request size multiples as shown in "Web Server Test Size Multiples"; set the percent read/write distribution to 100 percent read and the percent random/sequential distribution to 100 percent random.
As for the hardware, we had, dare we say, an eclectic environment: Our storage JBODs comprised two Eurologic Systems SANbloc 2100s 2-Gbps Fibre Channel dual-loop optical JBOD enclosures; 28 36-GB, 10,000-rpm Seagate Technology Cheetahs with four 2-Gbps Fibre Channel drives; one IBM ProFibre storage array JBOD DF4000J; 36-GB, 10,000-rpm Seagate Cheetahs with 15 2-Gbps Fibre Channel drives. We also used two gigabit Fibre Channel switches, a Vixel Corp. 9000 Series 16-port switch, a Gadzoox Networks SlingShot 4218 18-port switch and a QLogic Corp. SANbox2 16-port switch. Our base server system comprised a Compaq ProLiant DL580 server with four 700-MHz Xeon Pentium III processors, 1 GB of memory and two 64-bit 66-MHz slots. It ran Microsoft Windows 2000 Server SP2.

After resolving a problem that at first appeared to be a performance issue, we found we really like Emulex Corp.'s LP9002L-F2. Because of this glitch, however, we could not include the Emulex HBA in our comparative review.

So what kept the Emulex card out of the review? In a nutshell, the LP9002L-F2 has quite a few more Fibre Channel buffer credits than the other devices we tested. Buffer credits work like this: The sender keeps track of how many buffer credits (which translates into frames) the receiver has. When the sender has sent the full quota of frames, the receiver sends an authorization code, starting the cycle over. The LP9002L-F2 has a huge amount of buffer credits -- 64 -- while most other HBAs have four. However, our Vixel switch, used to send data to the other HBAs, did not acknowledge that the LP9002L-F2 has 64 buffer credits and filled just four of them, then stopped. The LP9002L-F2, having not received its quota of buffer credits, would not send the authorization for more data until the time-out period had expired, then the cycle would start again. This caused an approximately 16-MB-per-second performance gap between the LP9002L-F2 and the other HBAs we tested. We brought this problem to the attention of Emulex engineers, who re-created the test in the company's labs and confirmed that the problem lay with the buffer credits and the Vixel switch. Emulex and Vixel have worked together on a fix, and Vixel will have released a patch by the time you read this. Once we figured out the problem, we hooked up the QLogic SANbox 2 switch and ran the maximum throughput test. The performance of the LP9002L-F2 was in line with the other switches in the test.

Emulex Performance


The LP9002L-F2 was easy to set up, and the BIOS has quite a few features for the advanced Fibre Channel user. The interface, though a bit clumsy, was very serviceable, letting us configure any number of LP9002L-F2s, making multiple adapter configurations easy. The included software, lputilnt, simplifies such tasks as updating the adapter BIOS, and the unit does not require the use of an MS-DOS boot disk, as the other HBAs tested do. Another nice thing about the lputilnt utility is that it is installed with the driver. You do have to do a bit of searching, but once you have it, the utility is worthwhile, offering a wealth of information about adapter firmware revision levels, driver revision levels, PCI registers, statistics and counters, and other information that makes the storage geek's heart flutter. Emulex also offers an MD2 faceplate for low-profile installations, though the LP9002L-F2 box did not come with the MD2 faceplate inside, as Adaptec's did.

Finally, the Emulex unit sports a CD containing documentation for all the company's Fibre Channel HBAs and hubs, as well as a copy of Netscape Navigator 4.08. This documentation is stored in HTML and is easy to navigate and use. In many ways, we prefer this setup to the standard PDF document.

One of the things that really impressed us about the Emulex unit was that it remained competitive with the other cards in all the other tests, despite the buffer-credit issue. Buffer credits become very important as distances increase, and the LP9002L-F2, with its extra buffer credit capacity, is an excellent choice for long-distance applications, even those in excess of 10 kilometers. The LP9002L-F2 is a high quality card with good speed and support.

Fibre Channel gives us a huge mass of new terms, acronyms and English derivatives. Imagine that you distilled the technology sector's proclivity for acronyms and naming conventions into one thick, cloying liquid -- you'd have the terminology used to describe Fibre Channel.


For example, FC-AL means Fibre Channel arbitrated loop. Every Fibre Channel "end" device -- hard disks, tape drives or host bus adapters, for instance -- has a connection called a port. There are two kinds of ports: node ports and node-loop ports, which are abbreviated as N_ports and NL_ports, respectively. An N_port is the port by which a Fibre Channel device communicates to fabric port on a switch. An NL_port is an N_port that is capable of communicating on an arbitrated loop.


On the switch side of things, there are fabric ports and fabric-loop ports, abbreviated as F_ports and FL_ports, respectively. N_port devices connect to F_ports on a switch for a fabric connection. NL_port devices connect to a switch port in FL_port mode or to another NL_port device to provide arbitrated-loop operations. And to make life a bit more difficult, there is also an F/NL_port (fabric/node-loop port), which, in a pinch, can provide certain fabric services to other NL_port devices.


And just when you think the insanity will end, there is L_port, which is a generic term for any Fibre Channel port that supports arbitrated-loop operation. So remember: Ns are on the end devices; Fs are on the switches; the term L_port is a generalization. And we all know what we think of generalities. Got it?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Understanding Fibre Channel Technology

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Understanding Fibre Channel Technology

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Understanding Fibre Channel Technology

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Understanding Fibre Channel Technology

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