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SAN Design: March 29, 2001 3:18 pm
53-0001575-01 BROCADE Technical Note Page: 27 of 31
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