HBAs: Why some are better than others


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Currently most HBA vendors including Emulex, JNI, LSI Logic, and QLogic offer this functionality in their driver software for some of their HBA product line. Atto Technology will begin to offer it in early 2003. However, not all vendors necessarily offer this for all OS platforms.

Veritas probably has the most hardware-storage or HBA-vendor-neutral solution with their Dual Multipathing (DMP) software. It works on most major operating systems with any storage array and with a combination of different vendor's HBAs. However, in order to utilize this piece of software, you need other Veritas software running on that server, possibly diminishing some of the desirability of their solution.

For the OS side of the house, both Novell and Microsoft have a failover driver for the current releases of their respective platforms. The major Unix players--Sun, AIX, Linux, and HP-UX to name a few--vary on their ability to offer a native failover driver so administrators need to check on the version of their Unix OS if they desire to use this feature natively in the OS. For the hardware side, most of the major storage vendors--EMC, Hitachi Data Systems, Hewlett-Packard, IBM, and Xiotech--also ship HBA drivers that provide this failover capability, but the availability of these drivers varies by OS and only works when connecting to their storage solution.

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In analyzing all of the solutions that failover and dynamic load-balancing offer, the hardware vendors seem to have more robust solutions than the ones provided by either the software or HBA vendors. The hardware vendors frequently offer the dynamic load balancing as well as the failover, plus some other nice extras for troubleshooting SAN and application performance problems.

Right now, no one source currently exists where you may obtain a driver that provides failover capability that works regardless of the OS, storage or HBA. You'll need a good understanding of the environment into which you are deploying it, so you can select the correct HBA driver to get the functionality you desire.

The ABCs of HBAs
A is for Adapter Fibre Channel (FC) HBAs support both 1Gb and 2Gb speeds. The main bus architecture today is PCI, although it appears PCI-X will replace it in 2003 while SBUS is history. Almost without exception, all HBAs shipping today support the main FC protocols. The HBA naming convention of using World Wide Names (WWNs) is usually initially misunderstood until one realizes that it's the unique identifier of the HBA. And when it comes to connecting to a SAN, HBAs may use either copper or fiber optic cabling for connectivity.

B is for Bias HBA vendors try to differentiate their products mainly by features and price. For example, Atto Technology Inc.'s HBAs generally lack cutting edge features, but cost less. Emulex places a high emphasis on HBAs that have features supporting the increasingly higher speeds and distances SANs cover. JNI places more emphasis on intelligent switching within the HBAs, while LSI Logic touts Interrupt Coalescing, which allows you to tune for system/application performance while lowering server CPU requirements. Meanwhile, QLogic has built more functionality into their HBAs to better manage the new protocols that already run on FC such as FC Tape and virtualization.

C is for Conceptual Some new technologies are emerging within the SAN space while others are fading into the background. InfiniBand is one technology that glitters but is no longer gold in the eyes of the vendors. WWN spoofing appears headed for prime time in 2003 which will likely prompt the rise of more security in the SANs as well. Adding standards-based SAN management capabilities also hits close to home with all of the vendors. Their customers are no longer just asking for this functionality but are in some cases demanding compliance with emerging open standards. Yet without exception every vendor sees this as a positive as they view this opening more markets for their products.

Data buffers
Another feature that's built into all HBAs but at different capacities is data buffers and the related buffer credits. Emulex believes the importance of data buffers has risen for three reasons: The speeds of the HBAs have increased, the distance data must travel on SANs has increased and more environments have more heavily loaded PCI buses. Emulex says that without a large data buffer, a heavily loaded PCI bus could force the FC link to stop delivering data until the congestion clears.

Since one of the driving reasons for FC-SANS was FC's ability to handle large block transfers, factors such as distance or speed increases and both need to be weighed if the HBA is deployed into such an environment. Here's where Emulex claims they have an edge over their competitors. They have built a buffered architecture into their cards that supports up to 64 buffer credits of 2Kb each, which is significantly more compared to another vendor such as LSI Logic, whose PCI-X chips only contain 16 2Kb frame buffers.

As SANs move to 2Gb/s, Emulex alleges twice as many buffer credits are needed to achieve the same link utilization since the data transmit time is cut in half. They believe this will only be further amplified as FC speeds move to 4Gb, and then 10Gb. In long-distance SANs, higher buffer credits are also needed to accommodate the longer latency periods between the time the data is sent and received. In these circumstances, buffer credits on an HBA may become a deciding factor in the selection of one HBA over another in these environments.

Context switching
JNI is the primary vendor promoting this context switching. They define context as "the processing state and data memory structure used to execute a SCSI or FC protocol command." This means that the header information of the FC protocol carries information about the FC frame and its content. This becomes important if the HBA is to intelligently recognize the frame header information and act on that information.

According to JNI, you don't have a SAN-ready adapter if it can't perform this function. JNI defines a SAN-ready adapter as one that can route a FC header within five to 10 microseconds. In order to route this header in that time frame, it actually has to act on the FC packet prior to receiving the entire packet off of the FC link. For an HBA to do this, it must intelligently recognize when a context switch takes place.

Emulex and LSI obviously see merit in this approach as their cards also utilize this technology. LSI's chips optimize inbound frame data flow by doing context switching in the hardware. Their firmware completes processing of the current inbound frame while the hardware reads the FC frame header and establishes the context for the next inbound frame. Emulex believes they have an advantage here because they feature the largest hardware context cache in the industry enabling the processing of up to 2,048 simultaneous I/Os immediately. By using their onboard HBA cache as opposed to the server cache, their HBAs minimize server interrupts, CPU utilization and PCI bandwidth consumption.

Future directions
What features can customers expect HBA vendors to ship next? At Storage Networking World in Orlando, FL, Brocade and Emulex announced they would be working together to deliver centralized SAN management and enhanced security by extending the intelligence in the SAN fabric to include both the switching infrastructure and the HBAs. The two companies also plan to integrate joint functionality into the switch and HBA and architect and implement the Fibre Channel Authentication Protocol (FCAP) to include HBAs. In addition, third-party software developers will be able to write to the switch and HBA through the Brocade Fabric Access API, instead of developing for the HBAs and switches separately.

QLogic says it will have multiple announcements about HBAs and virtualization as well. InfiniBand connectivity has been relegated to the back burner for now--QLogic said other (albeit unnamed) projects have been put in front of InfiniBand.

As opposed to InfiniBand, a hot topic for HBA vendors is the spoofing of World-wide Names (WWNs), which is similar to assigning a network or IP address to a NIC card. QLogic already provides this spoofing functionality on a custom basis and anticipate spoofing to be a routine part of their standard driver package sometime in 2003. Atto would only say they were working with OEMs on this technology, and LSI Logic said that if it did deploy this technology it would be at the chip firmware level.

While WWN spoofing has management and routing benefits, it also opens up a Pandora's box on the SAN, similar to what has occurred in the IP networked world. Since WWNs would be assigned with human intervention, a logical question to ask is what happens if a server attempts to connect to a SAN where it's using the same WWN as another server and, in so doing, gains access to another server's data? Depending on how your SAN is set up and what security measures are deployed, the results could vary from nothing to losing data.

When the vendors were asked about data encryption and what security was being built into the SAN to prevent this from happening, they all essentially pleaded the industry's version of the Fifth by saying they're bound by nondisclosure agreement. Atto Technology said they view security as very important and are trying to sort out what security should reside on the HBA. QLogic's and LSI Logic's answer was equally as vague, almost echoing Atto's words. All vendors except Emulex did cite it as important, and indicated they saw it as a feature, though QLogic primarily envisioned it as a feature in their iSCSI cards.

A role HBA vendors were more willing to discuss was their part in SAN management. The major open initiatives are SNIA'S common interface model (CIM), which is heavily sponsored by Sun, Microsoft's Web-Based Enterprise Management (WBEM) and the Bluefin initiative being heavily driven by EMC and Hp. All of these forums are being supported and participated in by the HBA vendors contacted. But more important than just participation, the HBA vendors are adhering to customer demands to deploy these standards in their products. With the next generation of SAN management and security rapidly evolving, companies can expect to find more ways to manage and improve their SANs through the HBA: this seemingly unspectacular component of the SAN.

Web Bonus:
Online resources from SearchStorage.com: "Ask the Expert: Multiple HBAs," by Chris Poelker.

This was first published in December 2002

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