PMC Goes Loopy

Here's the pitch: A standard Fibre Channel Arbitrated Loop (FC-AL) connects up to 126 host and storage devices, with storage devices daisy-chained together. As a command or a piece of data travels to a particular disk, a port-bypass controller forwards it along the loop, skipping each irrelevant device until the target disk is reached.

It's a fairly old concept, with bypass controllers already available from vendors such as Agilent Technologies Inc. (NYSE: A) and Applied Micro Circuits Corp. (AMCC) (Nasdaq: AMCC).

So what does PMC-Sierra Inc. (Nasdaq: PMCS) think it brings to the party?

For one thing, greater density: PMC's new PBC 18x2G controller delivers 18 ports. It also announced a four-port device called the 4x2G. Both support 2-Gbit/s speeds on each port and use technology from the 2-Gbit/s serializer-deserializers that PMC released last year (see PMC Joins SAN Chip Table).

Eighteen ports is significant in itself, because most bypass controllers offer only six, PMC officials say. The higher density allows for more compact -- and therefore more economical -- system designs. The chip takes up 1.69 square inches of board space and consumes 4.2 watts.The devices also add some intelligence by monitoring the bit-error rate of the data. If errors stack up beyond a user-programmed threshold, the controller will flag some higher-layer device that something's going wrong.

The controllers also include a crossconnect switch, allowing ports to be grouped into zones, in case particular banks of storage are intended for particular departments in the enterprise. When a disk is taken offline, the crossconnect could be used to reroute traffic to a replacement.

The crossconnect could come in handy should someone want to develop a cut-through architecture, one that can skip a shelf of disks if it knows the destination disk is on a different shelf. "It's a new concept that you'll be seeing [from vendors] in the next few months," says Peter Wong, strategic marketing manager at PMC.

Formal part numbers for the PBC 18x2G and PBC 4x2G are PMC8368 and PMC8372, respectively. PMC has begun sampling both controllers. They are priced at $65 and $21.

Craig Matsumoto, Senior Editor, Light Reading