A host bus adapter (HBA) is a circuit board and/or integrated circuit adapter that provides input/output (I/O) processing and physical connectivity between a host system, or server, and a storage and/or network device. Because an HBA typically relieves the host microprocessor of both data storage and retrieval tasks, it can improve the server's performance time. An HBA and its associated disk subsystems are sometimes referred to as a disk channel.
HBAs are typically defined by interconnect technology, speed, port count and system interface. An HBA is sometimes called an HBA card. The HBA card often plugs into the PCI Express (PCIe) slot of a server. Other HBA form factors include mezzanine cards for blade servers.
Although the term HBA applies to a variety of interconnects, it is most commonly used with storage protocols such as Fibre Channel (FC) and serial-attached SCSI (SAS). A SAS HBA is a type of Small Computer System Interface (SCSI) HBA, but the term SCSI HBA is no longer in widespread use. A SCSI HBA typically is associated with parallel SCSI, a once popular data transfer technology that has largely been displaced by faster SAS.
Additional types of adapters that can connect a host system to storage and/or network devices include the following:
- Network interface card (NIC): Enables connectivity and data transfer between hosts and network devices over an Ethernet network. Alternate names include Ethernet adapter and Ethernet network adapter.
- iSCSI adapter (also known as iSCSI HBA or iSCSI NIC): Provides storage area network (SAN) connectivity over TCP/IP and Ethernet network infrastructure, and offloads the iSCSI and TCP/IP processing to the adapter to speed performance.
- Converged network adapter: Combines the functionality of an FC HBA and TCP/IP Ethernet NIC; supports local area network and FC SAN traffic.
- Host channel adapter (also known as InfiniBand adapter): Enables low-latency data communication between servers and storage over lossless InfiniBand networks; also used as server-to-server interconnect when servers are used for both application hosting and storage. Use cases include high-performance computing, data analytics, cloud data centers, and large-scale Web and trading applications.
- Remote Direct Memory Access over Converged Ethernet NIC (also known as NIC with RoCE): Facilitates data transfer directly between the application memory of different servers, without CPU involvement, to accelerate performance on lossless Ethernet networks. Supports faster data transfer than an Ethernet NIC. Typically used in financial, high-transaction database, storage and content delivery networks.
Fibre Channel host bus adapters
A Fibre Channel HBA enables connectivity and data transfer between devices in an FC SAN. An FC HBA can connect a host server to a switch or storage device, connect multiple storage systems, or connect multiple servers when servers are used as both application hosts and storage systems. SAN management software recognizes the HBA as the connection point.
Manufacturers of FC HBAs generally update their products in line with increases in the data rates of FC network technology. Fibre Channel products first became available in 1997. FC HBAs have progressed at rates of 1 gigabit per second (Gbps), 2 Gbps, 4 Gbps, 8 Gbps and 16 Gbps (also known as Generation 5 or Gen 5). The FC roadmap extends to 32 Gbps (Gen 6) and 128 Gbps, which uses parallel FC to stripe four lanes of 32 Gbps FC and create a single link of 128 Gbps. The initial use case for 128 Gbps FC is expected to be inter-switch link connectivity.
FC HBA manufacturers generally enhance products with additional features as they update to newer generations of FC technology. Improvements over the years have included data integrity to prevent on-the-wire corruption in database environments, and expanded support for virtualization to increase the density of virtual servers.
The market-dominant manufacturers of FC HBAs have been QLogic and Emulex. (Avago Technologies announced on Feb. 24, 2015 an agreement to acquire Emulex.) Additional FC HBA manufacturers include Atto Technology.
SCSI adapters/SCSI HBAs
A SCSI adapter, or SCSI HBA, facilitates connectivity and data transfer between a host and a peripheral device or storage system as defined by the SCSI set of American National Standards Institute standards for I/O interconnects. A plug-in HBA card typically initiates and sends service and task management requests to a target device, such as a storage drive or array, and receives responses from the target. The terms SCSI adapter and SCSI HBA generally refer to parallel SCSI, the predecessor to SAS.
Parallel SCSI devices are connected to a shared bus. The maximum parallel SCSI speed of 320 megabytes per second (MBps) is considered too slow to address the demands of modern computing systems, and performance often degrades as more devices are added to the shared bus. Parallel SCSI HBAs are viewed as outdated technology. Major manufacturers have discontinued production of parallel SCSI HBAs.
SAS was developed to address the limitations of traditional parallel SCSI and allow for higher speed data transfers to and from computer storage devices. Like parallel SCSI, SAS uses the SCSI command set, but the method of data transfer is different. SAS is a point-to-point serial data transport protocol. The introduction of SAS ushered in new terminology to describe the adapters, cables and connection options.
A SAS HBA typically connects a server or workstation to a storage device such as a hard disk drive, solid-state drive, JBOD device or tape drive. SAS HBAs are able to connect to single- or dual-port storage devices that are compatible with the serial ATA or SAS interface.
Vendors such as Dell, Hewlett-Packard and IBM sell entry-level storage arrays that support a SAS SAN fabric and enable direct connections to servers equipped with SAS HBAs. Such entry-level SAS storage arrays eliminate the need for network switches.
A SAS HBA can also connect to a SAS switch to enable connections between multiple servers and external storage. The use of switched SAS is not as common as SAS HBA-based direct connections between the server and storage array.
SAS bandwidth started at 3 Gbps and advanced to 6 Gbps and 12 Gbps. Each new generation of SAS also brought additional functionality such as the ability to run longer distances of cable.
SAS HBAs are typically less expensive than FC HBAs. However, the FC SAN offers higher performance and greater configuration options than a SAS environment. Director-class FC switches can support more than a thousand ports.
Major SAS HBA manufacturers include Atto Technology, Avago Technologies (through its acquisition of LSI), and PMC-Sierra (through its acquisition of Adaptec). Hewlett-Packard also makes a SAS HBA card using components from PMC-Sierra.
Differentiators between SAS HBA products include the supported SAS speed, data transfer rate, port count, PCIe bus type and power consumption.
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