IBM manual Switched FC-AL advantages, 11 DS8000 disk enclosure

These problems are solved with the switched FC-AL implementation on the DS8000.

Switched FC-AL advantages

The DS8000 uses switched FC-AL technology to link the device adapter (DA) pairs and the DDMs. Switched FC-AL uses the standard FC-AL protocol, but the physical implementation is different. The key features of switched FC-AL technology are:

￿Standard FC-AL communication protocol from DA to DDMs.

￿Direct point-to-point links are established between DA and DDM.

￿Isolation capabilities in case of DDM failures, providing easy problem determination.

￿Predictive failure statistics.

￿Simplified expansion; for example, no cable re-routing is required when adding another disk enclosure.

The DS8000 architecture employs dual redundant switched FC-AL access to each of the disk enclosures. The key benefits of doing this are:

￿Two independent networks to access the disk enclosures.

￿Four access paths to each DDM.

￿Each device adapter port operates independently.

￿Double the bandwidth over traditional FC-AL loop implementations.

In Figure 2-11each DDM is depicted as being attached to two separate Fibre Channel switches. This means that with two device adapters, we have four effective data paths to each disk, each path operating at 2Gb/sec. Note that this diagram shows one switched disk network attached to each DA. Each DA can actually support two switched networks.

server 0	Fibre channel switch	server 1
device		device
adapter	Fibre channel switch	adapter
Figure 2-11 DS8000 disk enclosure

When a connection is made between the device adapter and a disk, the connection is a switched connection that uses arbitrated loop protocol. This means that a mini-loop is created between the device adapter and the disk. Figure 2-12 on page 34 depicts four simultaneous and independent connections, one from each device adapter port.

Chapter 2. Components 33