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The FAIS Initiative – Standardizing Fabric Switch APIs
The FAIS initiative intends to establish standard APIs for fabric switches that would be supported across vendor lines. This would enable a virtualization software vendor, for example, to create code that would interface with products from McDATA, Brocade, or other switch vendors, and either be hosted directly on the switch itself or on a SAN-attached appliance.
The consensus among vendors that APIs should be standardized is driven by a common desire to interoperate with a wide variety of virtualization applications. Even Brocade, despite its less than stellar track record on interoperability, is fully supportive of FAIS. This unexpected openness will give customers more flexibility in selecting what types of enhanced services they need and what infrastructure to drive them on.
A FAIS interface is predicated on the separation of control and data paths. The control path is the channel for traditional SCSI command sets and supports both initiator and target mode. The control path may terminate within a fabric switch (e.g., an internal processor running virtualization code) or be redirected to an appliance. The data path is for common SCSI read/write operations, although with FAIS the data path is an abstraction from physical storage.
This enables, for example, a fabric switch to connect to multiple storage arrays and represent them as a single storage pool for normal SCSI transactions. This abstraction layer for the data path through the fabric necessarily requires an interface for discovery and configuration by virtualization software, as well as a means to pass errors or exceptions from the data path to the control path for resolution.
As currently stated in the FAIS charter, the fabric API should be portable to different operating systems to provide greater flexibility in deployment. Coding will thus be done in standard C language to facilitate cross-platform development. How, specifically, fabric switch vendors may elect to host FAIS-enabled virtualization or other services is vendor-dependent.
Some announced offerings are essentially bladed PCs that slot into a switch chassis. This has the advantage of off-the-shelf time to market, but may create performance bottlenecks. Other offerings (Aarohi, for example) are silicon solutions that offer both performance and a compact footprint.