FCLC Boosts Interoperability Testing

Posted on October 01, 1998

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FCLC Boosts Interoperability Testing

The Fibre Channel Loop Community and its partners are working hard to ensure interoperability among products from different vendors.

By Howey Chin

A storage area network (SAN) is a data-centric network that increases capacity, improves data access for clients, and provides functions essential to enterprise data management such as backup and restore, hierarchical storage management (HSM), remote data mirroring, etc. Unless SANs are deployed, LAN improvements will be unable to offer significant performance benefits for client data access.

A key item for successful SAN deployment is interoperability, the scope of which is often misunderstood. Interoperability testing can be conducted in two ways.

A narrow, vertical approach will result in rapid deployment of point solutions, but may preclude more innovative solutions in the future. A horizontal approach will result in the proliferation of innovative solutions for different market needs, yet at a slower pace.

A vertical approach to interoperability predefines the application. In doing so, a particular application may be usable more quickly, but it also may preclude the extension of a network technology to other applications.

Horizontal approaches to interoperability segment--or layer--the problem. This enables parallel development of many applications onto a common layer by a diverse group of unrelated developers. Taking this layered approach to developing interoperability and solutions enabled LANs to move from file and print sharing to inter-networking.

Fibre Channel`s unique addressing hierarchy and multi-protocol transport characteristic permits the best of both worlds relative to interoperability and deployment. Fibre Channel is not an "all or nothing" technology. End users can deploy selected portions of the technology to solve pressing storage problems immediately. The flip side is that it presents unique challenges to interoperability testing.

The multi-protocol Fibre Channel layers correlate to the ISO reference model (see Figure 1). The multi-protocol transport enables highly scalable server solutions and makes it essential to take the horizontal layered interoperability approach. A vertical approach could preclude implementations requiring other protocol services. Fibre Channel interoperability testing is conducted in a manner that permits vertical solutions while addressing a layered model to enable future innovation.

The Fibre Channel Loop Community (FCLC) has sponsored several Interoperability Plugfests, most of which have been hosted by Interphase Corp. The most recent PlugFest occurred earlier this month, October 11-15. Interphase established a separate controlled access facility many years ago at its site in Dallas to encourage network developers to co-operate on product interoperability.

A marketing organization, the FCLC (www.fcloop.org) recognized that quality testing needed strong guidance and technical management to achieve its goals. For these reasons, FCLC turned to the InterOperability Lab (IOL) of the University of New Hampshire (www.iol.unh.edu) and contracts its skilled personnel to establish the test plans and handle the on-site details of test operations.

The goal of the PlugFests is to forward Fibre Channel interoperability in the larger sense of robust network and link layers that facilitate building multi-protocol SAN services, rather than strict conformance testing. Conformance to the Fibre Channel standard at the link layer is a crucial requirement for interoperability, as is non-interference among the separate protocols. Remember: What were once previously separate protocols on their own transports now share the same link layer in Fibre Channel.

Testing at the FCLC Interoperability events looks principally for corner cases and error situations that exercise an exhaustive number of error transition states. Root cause analysis is performed to isolate failure or non-conformance to a communication layer, with particular interest in the link layer.

Fibre Channel permits multiple transport protocols to share the same link layer. This unique attribute enables Fibre Channel to accelerate, scale, and add resiliency to server applications while occupying fewer PCI slots. The facilities available in the presentation and session layers of current servers do not adequately address some of the configurations possible with Fibre Channel. This is an inadequacy that can cause test configurations to fail at the application layer. If this happens, root cause analysis is used to determine whether the Fibre Channel layer is still functional, even if the application is not.

What constitutes an operational Fibre Channel configuration? Primarily, the configuration has to be able to recover from all possible combinations of dynamic (unexpected) perturbations of a network (e.g., initial power-up, addition of a new node, movement of a node, and changes to the network not resulting in a movement or an addition).

Recovery means that all the nodes in the network resolve themselves to a unique address, and each node is aware of that unique address if it has a need to communicate to it. Although an application may no longer be operating, the link layer must be in the ready-to-communicate state. Most of all, a failure at one node should not cause another node to fail.

Interoperability testing focuses on network recovery of two key network properties: address resolution and dynamic discovery. Address resolution is the manner in which devices acquire a unique network address. Dynamic discovery is the manner in which the network detects a configuration change and re-detects the addresses of participating devices.

Fibre Channel is built on two cooperating address spaces: the loop and the fabric. Fibre Channel Arbitrated Loop (FC-AL) is a simplified, sparse address space that can be cascaded through a fabric services hierarchy of device connections (see Figure 2).

FC-AL allows the connection of up to 126 L_Ports, without need for an intervening network routing element. The sparse FC-AL address space resolves addresses and efficiently performs dynamic discovery using the loop initialization protocol (LIP). Rather than polling or broadcasting everyone that a node is participating on a loop, FC-AL automatically detects a configuration change and causes the address tables to be updated. The mechanism for informing all participants on a loop of a change is an FC primitive signal called a loop initialization primitive (LIP). Any node detecting a network change may issue a LIP. The LIP provides a prioritization of address assignments, which restores the network to an address map that is either identical to, or the closest possible match, to its previous address map. This approach minimizes transport protocol disruption.

Fabric services provide extended addressing using a name server (a.k.a. directory server) and dynamic discovery via a state change notification process. A combination fabric/loop node, referred to as a FL port, provides the bridging services necessary to connect L_ports to the extended fabric space.

Once a stable network configuration has been established, efficient data transport is readily sustainable. Dynamic network reconfigurations and multi-protocol co-existence are most problematic when testing, which explains why the conformance and robustness of the addressing and discovery implementations are heavily stressed by the interoperability testing. Addressing and discovery are tested within the FC-AL space and the fabric space, and separate testing is conducted on the bridging and fabric services, which are necessary to cascade FC-AL loops.

By focusing on link layer conformance and transport protocol co-existence, Fibre Channel interoperability testing ensures the availability of a robust link and network layer. Testing allows host, target, and infrastructure suppliers to ensure that their products are interoperable.

With an abundant range of vendors meeting the interoperability criteria of this new storage infrastructure, software developers can provide innovative solutions for storage area networks through the session and presentation layers. When industry collaboration emerges for a common SAN Services layer, interoperability testing will expand to encompass this area as well.

The Interoperability PlugFests are based on several factors:

- FCLC provides a cooperative and confidential environment.

- Developers can increase their awareness of how layered interoperability functions and use the results to resolve any problems detected.

- Technical resources are available on-site from the University of New Hampshire.

- ANSI T11 representatives are present to provide feedback to the standards committee.

- Interphase has a spacious facility that is wired for gigabit Fibre Channel and enables rapid re-configuration of the test configuration.

- Analyzer vendors provide the ability to capture network events so root cause analysis can be performed off-line.

The level of cooperation among participants is high. Even though they are competitors, member companies recognize the value of working together to resolve issues before they turn into problems at customer sites. The results speak for themselves: Considerable advances in interoperability have been made in the past year.

Fibre Channel can be used to deploy SAN solutions today to solve vertical storage problems. The interoperability effort ensures a robust network and link layer for SAN services developers to provide new capabilities to enhance storage and server applications. Early Fibre Channel adopters can rely on the abity to leverage current investments in Fibre Channel technology to deploy new SAN capabilities.

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Figure 1: The multi-protocol Fibre Channel layers correlate to the ISO reference model.

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Figure 2: The FC-AL address space can be cascaded together through a fabric services hierarchy of device connections.

Howey Chin is an FCLC board member and heads the Interoperability Steering Committee for the FCLC. He is also the chief strategic officer at Gadzoox Networks, in San Jose, CA.


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