User`s guide

Chapter 1. Implementing Fibre Channel host adapter cards 5
򐂰 Feature code 3023 — This is a short wave laser adapter that includes a 31-m
(100-ft) (50-micron) cable with duplex connectors. When you use the 3023
adapter to perform a FICON channel attachment, you must use the cables for
FICON. The adapters cannot be shared with any Fibre Channel protocol
attachments.
Because the 3023 uses one of four slots in one of the four I/O bays, you can
have a maximum of 16 adapters in the ESS. This allows you to have a maximum
of 16 FICON interface attachments. If the attachments are all point-to-point, you
can attach directly to 16 FICON channels. If you attach to a switch or director,
you can attach a maximum of 128 FICON channels per ESS FICON adapter. For
this scenario, you must be able to attach to a number of hosts. The ESS allows
256 logical paths per FICON link (compared to just 64 for ESCON), 128 logical
paths per logical subsystem, and 2048 logical paths for each ESS.
Before FICON, you could only do a Fibre Channel connect for Fibre Channel
protocol with feature code 3022. Feature code 3023, with a 9-micron single mode
fiber-optic cable, increases the point-to-point distance from 500 m to 10 km.
The increased distance provides greater configuration options with IBM S/390 or
zSeries processors with FICON host adapters.
1.2.2 Attachment considerations
This topic describes some things you should consider before you configure your
system with a FICON interface.
1.2.3 Setting up ESCON and FICON links
If the system requires x ESCON links, where x is the number of links to get the
performance and availability attributes you want, you must consider the number
of ESCON you need. For example, you can map four ESCON links to a single
FICON link and maintain approximately equivalent performance. If the ESCON
channel use is low, you can map six or eight ESCON links to a single FICON link.
1.2.4 Multipathing for ESCON and FICON
Consider the difference between the path groups when you compare FICON to
ESCON. For example, for ESCON, you can configure four or eight paths per
path group from a host to an ESS. For ESCON, you want at least four paths in
the path group to maximize performance. Most ESCON controllers implement
channel command execution that partially synchronizes the lower DASD
interface with the upper channel interface. This channel command only allows
you a very short time to reconnect. The consequence is reconnections that fail.