Defining shared channel paths

Before defining shared channel paths, consider the following:

• All channel types supported by the z17 can be shared. On CF only models CL5, CL6, CS5, and ICP channel paths cannot be shared.
• A failure in a shared channel path or I/O device can affect more than one LP; therefore, critical I/O devices (for example, DASD containing vital data sets) still need multiple channel paths. You can provide multiple shared channel paths (up to 8) to critical I/O devices.
• Using shared channel paths does not reduce the number of logical paths needed at a control unit. A control unit requires a logical path for each active LP that can access I/O devices through a shared channel path.

There are three possible channel path modes:

shared

A channel path that can be configured online to one or more LPs at the same time. One or more LPs can access I/O devices at the same time using this channel path. Spanned channel paths are shared by LPs in multiple logical channel subsystems (CSSs). Unspanned channel paths can only be shared by LPs in the same CSS.

reconfigurable

An unshared channel path you can reconfigure offline from one LP, then online to another, within the same CSS. Only one LP can access I/O devices on this channel path at a time.

dedicated

An unshared and non-reconfigurable channel path. Only one LP can access I/O devices on this channel path.

You cannot mix unshared and shared CHPIDs to a device.