Host bus adapter (HBA) architecture explained

HBAs are integral pieces of a SAN environment -- they connect the server to the SAN -- but few storage administrators know how to configure them.

Even though a host bus adapter is integral to effective enterprise data storage, some storage administrators, when they first hear the term, think it's a type of business degree. But they soon realize that they need to be versed in host bus adapter architecture and how host bus adapters can be used to optimize a SAN infrastructure.

A host bus adapter (HBA) is a hardware device, such as a circuit board or integrated circuit adapter, that provides I/O processing and physical connectivity between a host system, such as a server, and a storage device. The HBA transmits data between the host device and the storage system in a SAN and relieves the host microprocessor of the tasks of storing data and retrieving data. The result? Improved server performance.

HBAs are most commonly used in Fibre Channel SAN environments and are also used for connecting SCSI and SATA devices. The emergence of iSCSI has led to the development of another type of host bus adapter, the Ethernet HBA.

HBAs integral to SANs

HBAs are integral parts of a SAN environment. According to Bob Laliberte, an analyst at Enterprise Strategy Group, "Typically the HBA will be recognized by the SAN management software. In order for a server to be provisioned storage, it needs to have a connection to that storage. The HBA is one of the components that need to be configured properly in order to provide that connection."

When selecting an HBA, storage managers should evaluate features such as performance, reliability, security, power and server virtualization capabilities, says Amit Vashi, vice president of marketing at HBA provider QLogic Corp. He says that another criteria, particularly for enterprises running servers from multiple vendors, is whether an HBA has broad operating system support. Storage managers should look for an HBA that supports all hardware platforms and operating systems.

Organizations should also select an HBA technology platform that provides a common driver architecture across multiple generations, says Scott McIntyre, vice president of customer marketing at HBA vendor Emulex Corp. "This ensures seamless management of all the HBAs throughout the SAN, which is critical in data center environments with hundreds or thousands of servers attached to external storage," he says.

Does it make sense to implement HBAs from more than one vendor? According to Laliberte, standardizing on a single HBA vendor simplifies the management of these devices. "Centralized management in large environments -- think hundreds or thousands of servers, each with multiple HBAs -- is critical," he says. "Trying to upgrade them all, either a patch or software enhancement, can be very difficult. Centralized management software from HBA vendors can help."

Ensuring proper interoperability of HBAs is a challenge, Laliberte says, but that task should be taken care of by the vendors.

HBAs for Fibre Channel SANs currently support data rates of up to 8 Gbps, but future products will support rates of 16 Gbps and 32 Gbps. "In general, they are getter faster and costs are remaining relatively flat for the increased performance," Laliberte says. "Overall, there is more effort being put into them to make them easier to manage: single console, automated patch and upgrade capabilities." Vendors are also trying to place more intelligence in the HBA for greater manageability, he says.

Other trends in the HBA arena include increased security capabilities and the support of server virtualization. Offering security technology, such as encryption and authentication, has generally not been a priority with HBAs, Vashi says. But that will change as it becomes more common to run Fibre Channel over Ethernet (FCoE).

Virtualization poses challenge to HBA vendors

Today's HBAs must deal with virtualization, particularly when it comes to gaining visibility into virtualized server environments, Laliberte says. Virtualization adds a layer of complexity to HBAs, "because it allows multiple applications to be abstracted. There is no longer a one-to-one relationship with application to server. In many cases, there could be five or more applications on a single server sharing an HBA," he added.

And with the mobility options available in virtualization, applications could actually be migrated from server to server, Laliberte says, making it more difficult to identify applications that require storage.

In today's virtualized environments, multiple virtual machines can be loaded onto a single physical machine with one or two HBAs, Laliberte says. In the past, with a one-to-one (i.e., one application to one server) infrastructure, management tools would associate the HBA to the application manually. But now there can be many applications going through a single HBA, and the difficulty arises in trying to manage that environment. How do you know where the applications are? N-Port ID Virtualization or NPIV is a technology now being adopted in HBAs that enables the HBA to create a separate multiple logical ports for the multiple virtual machines that can then be easily identified as they migrate between servers.

The increasing popularity of server virtualization and the growing use of blade servers are driving demand for storage, and that translates into greater need for SAN connectivity solutions, such as HBAs, McIntyre says. "We are seeing additional server tiers tapping into SANs because of these trends," he adds.

The leaders in the HBA market are acknowledged to be QLogic and Emulex. QLogic supplies a range of storage networking products, including Fibre Channel HBAs for standard servers and blade servers, Fibre Channel switches, Fibre Channel stackable switches, iSCSI HBAs and iSCSI routers. The company also provides InfiniBand switches and InfiniBand host channel adapters for the emerging high-performance computing market. Emulex offers an array of standard Fibre Channel HBAs, supporting data rates from 2 Gbps to 8 Gbps. The company also sells HBAs for blade servers. Emulex also provides HBA management software, such as HBAnyware, a management suite that enables organizations to update and manage all the HBAs in a SAN, either locally or remotely.

According to Laliberte, there's not a lot of difference between QLogic and Emulex HBAs. Both vendors seem to be on almost an identical product development track. Laliberte says he would give Emulex a slight edge in ease of use by virtue of its HBAnywhere software. However, he noted, QLogic offers a wider range of products, with SAN switching, a bigger bet on iSCSI and InfiniBand, and so can offer SAN starter kits and drive into the high-performance computing (HPC) market.

Other HBA vendors include LSI Corp., Atto Technology Inc. and Brocade Communications Systems Inc., which entered the HBA marketplace in 2007 with devices for Fibre Channel SANs.

All these vendors can expect to see increased demand for HBAs. A 2007 report by Dell'Oro Group forecasts that shipments of HBA ports will grow significantly over the next five years as blade server producers shift the manufacturing of HBA cards to vendors, such as Emulex and QLogic.

About the author

Bob Violino is a business and technology freelance writer based in Massapequa Park, N.Y. He can be reached at

This was first published in April 2008

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