Brocade Communications Systems 53-0001575-01 manual Brocade Technical Note

SAN Design: March 29, 2001 3:18 pm

width of 100 MBytes/sec. Thirty disks attached to a hub on a single physical loop will not perform as well as 5 disks attached to 6 switch QuickLoop ports. Other advantages are:

•Loop tenancies can occur in parallel on different looplets. A loop tenancy occurs when a device takes control of the loop to perform I/O and I/O to any other loop device is restricted. In most loop implementations only one device is allowed control (tenancy) at a time.

•Faults are isolated to a looplet [Looplet: a single switch port with attached loop devices that are part of larger logical loop], instead of affecting the entire loop

•The switch management tools and port statistics and debugging data are available for monitoring and management of the QuickLoop

The switch will isolate misbehaving devices on a given port from the rest of the switch attached devices and will not propagate LIPS from a misbehaving device to other devices sharing a single logical loop. [Note: managed hubs provide a similar capability.]

It is possible to use a switch in QuickLoop mode to connect JBODs and other private devices without having to change software drivers and have this be a plug-and-play solution. Software license upgrades to the QuickLoop switches can be used to provide for full fabric sup- port when users are ready to migrate to fabrics.

Translative mode. This addressing option is built into the Fabric OS™ for SilkWorm. It allows for public devices to see and talk to private devices. The private devices (typically disks in a JBOD attached to a switch FL-port) would normally only have 8 bit addresses and be missing the Domain and Node address bits required for a public device. Translative mode provides a pseudo 24 bit address for these devices and presents this “phantom address” to a public devices (typically a host) that wants to perform I/O to the disks. The switch detects when traffic has a destination ID of this pseudo address and the FL-port translates the public address back into the ALPA for the device on the loop (and vice-versa). There are limitations in total number of devices that can be on a loop in translative mode:

•SilkWorm 1000: 31 devices can have phantom public addresses in a single loop

•SilkWorm 2000: 125 devices can have phantom public addresses in a single loop

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