SAN management update: How the SM HBA interface will help manage it all...

Enterprise Networks & Servers, Jul 2005 by Douglas, Chet

Serial ATA (SATA) and Serial Attached SCSI (SAS) controllers and peripherals continue to drive improvements in storage performance and decrease the cost and complexity of setting up a storage network. With the addition of these new storage protocols, it becomes even more important to be able to manage and configure multiple technologies using a common method. When inexpensive SAS expanders are added to a SAS topology, it becomes possible to build enterprise-level redundant path storage networks, much like the more powerful and typically more expensive fiber-channel (FC) storage fabric technology. The similarities between FC and SAS make it desirable and advantageous to utilize the same storage management interface to manage both technologies.

By adding SAS and SATA functionality to a pre-existing, commonly used management interface, administrators can manage new protocols using a single technology. This requires not only less time to be spent managing storage, but in addition, management is less cumbersome and ultimately less expensive. This strategy also allows independent software and operating system vendors to utilize their existing investment in FC technology. Furthermore, adding these protocols to the existing interface will significantly speed its acceptance by the International Committee for Information Technology Standards (INCITS) Tl 1.5 storage management committee, which will accelerate its adoption by the storage industry.

Intel Corporation is currently authoring this new storage management API with the help from key storage industry participants. The new storage area network (SAN) management API, SM HBA, is based on the industry accepted FC HBA API and will allow software applications and operating systems to manage FC and SAS storage. To comprehend what SM HBA is and how it will revolutionize storage management, one must first understand its predecessor, the FC HBA API.

What is the FC HBA API?

The FC HBA API is a vendor-unique storage management software interface based on an earlier proprietary version of a FC Host Bus Adapter management API and written in the C programming language. Originally the FC HBA API interface was brought to the Storage Networking Industry Association (SNIA) to create an industry-accepted management API. The specification was later moved to the International Committee for Information Technology Standards (INCITS) Tl 1.5 committee and was approved as Version 1 of the FC HBA API.

The Version 1 specification supports managing direct connected FC HBAs, the local FC Ports (referred to as NxPorts) and the discovered NxPorts of the target devices found in the fiber channel fabric. The interface allows returning cumulative statistics for the NxPorts in the fabric and resetting those statistics at any time. This version also provided the ability to retrieve persistent bindings for discovered target devices. Persistent binding for a target device is the ability of the underlying storage infrastructure to consistently map a given FC World Wide Name (WWN) of the target device to a particular SCSI address. This insures that a consistent view of the fiber channel targets are surfaced through the FC HBA API, no matter where the underlying target devices might be found in the fabric. The other major functionality introduced in Version 1 of the interface was the ability to manage the FC fabric itself by providing basic extended link services (ELS) interfaces and the CT passthru interface that provides a mechanism for sending FC management requests to FC hubs, routers, and domain controllers found in a typical fabric.

Since the original specification was accepted by the storage industry, further improvements and additions were made to the specification in Version 2 of the FC HBA API. This second generation specification adds the ability to get and set target-persistent binding support as well as the ability to set target-persistent bindings. This version also adds the ability to register for and receive asynchronous event callbacks from the FC HBA API. This allows storage management applications that utilize this interface to receive notifications of state changes for existing HBAs, addition or removal of HBAs, addition and removal of target devices, Port and Phy changes, and statistic thresholds exceeded. The Version 1 statistics are improved with the addition of FC4 statistics for those ports supporting the FC-4 protocol. This version also adds support for single byte (SB) target devices.

Figure 1 - FC HBA API Object Model shows a simplified UML Class diagram for the FC HBA API. While the FC HBA API is not specifically an object-oriented design, it is still useful to treat it as such for showing the basic organization of the FC HBA API data and methods. Each object represents a logical grouping of attributes and methods to form an interface for each FC HBA API object. The FC HBA library object contains attributes describing the entire FC HBA API interface including the version of the FC HBA API. The library object contains methods to acquire a list of HBAs and handles to each HBA. The HBA handle is used to identify the HBA in most of the methods used by the FC HBA API. The HBA_ADAPT-ERATTRIBUTES object contains attributes of each local physical FC HBA found in the system. It provides methods to determine the number of FC NxPorts, or HBA_PORTATTRIBUTES and the SCSI target devices attached to each local Nxport of the FC HBA. NxPorts can be local HBA end ports or discovered FCP or SB ports. Attributes of the NxPort object includes a port type, such as an FCP port. The FC-3 management class provides attributes to describe FC hubs, routers, and domain controllers and methods to configure those devices.