Storage Area Networks: Designing and Implementing a Mass Storage System

8.3 FC-AL Hubs

The FC-AL hub is available in shortwave (S10) and longwave (L10) models. Both models have ten ports, and are available in standalone or factory-racked configurations. The AZ models are the factory-racked models.

8.3.1 Features

• The shortwave hub has ten non-OFC, shortwave optical transceivers.

• The longwave hub has nine non-OFC, shortwave optical transceivers and one non-OFC, longwave optical transceiver.

• Local retime and regeneration of transmit signals to prevent accumulation of jitter and improve the signal.

• Reliable, automatic bypass of failed nodes; dynamic recognition of newly added or removed nodes, with a controller in each port permitting the bypass of a port if the port fails signal validity tests.

• Active loop reconfiguration when a node to an arbitrated loop is added, removed, or moved.

• Plug-and-play capability, allowing the hub to connect to compatible servers and other FC-AL devices while they are operating. FC-AL devices can be added or removed while the hub is active.

8.3.2 S10 Shortwave Hub (HP A3724A/AZ)

The shortwave hub supports 10 non-OFC (non- open fiber control) shortwave FC-AL connections. In arbitrated loop topology, the data rates and wavelength between ports must be the same. The shortwave hub supports only gigabit shortwave to gigabit shortwave connections using fiber cables.

For the shortwave hub, Hewlett-Packard recommends 50 micron multimode fiber cable for new installations, but supports 62.5 micron multimode fiber cable with SC-style connectors in existing installations. Installations can mix 50 micron and 62.5 micron cables.

Using a 50 micron multimode cable, the shortwave hub supports distances up to 500 meters between a server host and the hub, between a hub port and a connected FC-AL device, and between two hubs. The maximum distance between a host server and FC-AL devices connected to cascaded shortwave hubs is 1500 meters .

8.3.3 L10 Longwave Hub (HP A4839A/AZ)

The longwave hub supports nine non-OFC, shortwave devices and a second longwave FC-AL hub. The longwave hub supports shortwave gigabit to shortwave gigabit connections from ports 1 through 9 using fiber cables. The longwave hub also supports a longwave hub to longwave hub connection from the longwave port.

For the longwave port, Hewlett-Packard recommends 9 micron single mode fiber cable. For ports 1 through 9, Hewlett-Packard recommends 50 micron multimode fiber cable for new installations but supports 62.5 micron multimode fiber cable with SC-style connectors in existing installations.

For ports 1 through 9, the longwave hub supports distances of up to 500 meters between the port and a connected FC-AL device. For the longwave port, the longwave hub supports distances of up to 10 kilometers between two longwave hubs.

When distance is a necessity, up to two HP FC-AL hubs can be cascaded, allowing greater connectivity distances between servers and storage devices, and further increasing the breadth of deployment options. For example, cascading two shortwave hubs allows distances of up to 1.5 km. And cascading two longwave hubs gives distances of up to 10 km, when attached to an HP-UX server. An additional 500 m can be added between the server and storage devices on either end of the hubs. This can add an additional 1,000 m to the whole SAN topology, for a maximum distance of 11 km.

The throughput and distance of Fibre Channel technology translate into increased flexibility for today s storage area networks, online transaction pro-cessing applications, and other installations where data availability and reliability are mission critical. With FC-AL hubs, campus and metropolitan SANs can be set up in widely separated nodes and still provide mirrored failover disaster recovery at gigabit speeds.

8.3.4 Fibre Channel Manager

Hewlett-Packard s Fibre Channel Manager is a device manager for the FC-AL hub. The tool is used for configuration, monitoring, and troubleshooting.

HP Fibre Channel Manager (FCM) is a client/server intranet application, installed on a machine designated as a management server. This machine monitors any hub connected to it, whether directly or as part of a cascaded chain. FCM uses a Web server to collect, store, and present data to the client (the machine designed as the management workstation). The management workstation employs an easy-to-use Web browser to view data presented by the server.

8.3.5 Plan the FC-AL Connections

The hub does not require drivers or specific versions of the HP-UX operating system, but FC-AL devices that connect to the hub do. Contact an HP sales representative for information on hardware and software requirements for the FC-AL devices you plan to connect to the hub.

1. Verify the loop cabling configuration is correct by comparing it to the cabling example in Section 8.3.5.1. Modify the network cabling map as needed.

   Note

   Incorrect wiring can lead to problems such as devices left off the loop and inaccessible by the server. Follow the guidelines below before starting.

2. Review the user -assigned loop ID (hardware address) of every FC-AL device to be connected to the hub and make sure that each ID is unique. Duplicate IDs on the loop can cause problems. In addition, each device has its own factory-assigned unique worldwide name .

3. Verify the connections between the hub port and the FC-AL mass storage device or the FC-AL host bus adapter are of the same wave type and speed. For example, plan to connect a port on the hub to a shortwave FC-AL device.

4. Document the planned connections in a cabling map.

8.3.5.1 Correct Cabling Examples

In a cascaded hub configuration, connect any port on the first hub to any port on the second hub. The following example includes all 18 nodes in the loop formed by FC-AL Device 1, Hub A, Hub B, and FC-AL Device 2. FC-AL Device 1 is connected to Port 1 on Hub A; Port 10 of Hub A connects to Port 1 of Hub B, and Port 10 on Hub B connects to FC-AL Device 2. In this configuration, Port 10 on Hub B can connect to any FC-AL device. This is just one example of cascaded hubs. The connection between hubs can occupy any combination of ports.

8.3.5.2 Incorrect Cabling Examples

Figures 8-14 through 8-16 are examples of incorrect cabling. For example: Do not cable together two ports on the same hub. Ports between the two connections will be eliminated from the loop.

Do not attach more than one cable between any two hubs.

Do not attempt to connect a hub to more than one other hub.