FICON considerations for IBM Z hosts

Edit online

Before you configure your system with FICON adapters for IBM® Z hosts, review considerations regarding the number of links, multipathing, and channel-path groups.

Multipathing FICON

With multipath mode operation, reconnections can occur on any path in a path group. Increasing the number of paths allows reconnections to occur in a more timely basis. If you use eight paths in path groups, you can increase the overall throughput.

FICON allows a multiplex of requests for different devices concurrently. There is no problem with reconnections occurring concurrently with other I/O operations on a single path with FICON. The number of paths in the path group depends on the throughput requirement. If it takes x paths to satisfy the throughput requirement, where x is the number of paths, set the path group to x.

Note: x must be a minimum of two and cannot exceed a maximum of eight.

Attaching to a FICON channel or a FICON channel-path group

When you attach multiple controllers to a channel, you are connecting serially. You can use a switch (director) for each controller or FICON channel that has a direct connection to the controller. I/O activity does not flow through all the other controllers before you get to the target controller. I/O activity goes directly to the target controller. When multiple controllers are connected to a channel through a switch, you create the logical equivalent of the parallel interconnection.

FICON® does not support a private connection. FICON performs frame (or packet) multiplexing. A configuration with the serially connected controllers communicates with the controllers simultaneously. It can multiplex I/O operations across all controllers simultaneously. No interface cycles are wasted because of a private connection. You can serially connect controllers with FICON without performance degradation.

You must also consider the implications of serially connecting disk drive control units with tape controllers. Tape performs much larger I/O operations at any instant in time. Therefore, even with FICON, when you run tape I/O, you can temporarily lockout some disk drive I/O operations. It is still better to connect tape and disk drives to different FICON channels.