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While a shared channel path can be shared by LPARs within a same LCSS, a spanned channel path can be shared by LPARs within and across LCSSs. 

By assigning the same CHPID from different LCSSs to the same channel path (for example, a PCHID), the channel path can be accessed by any LPARs from these LCSSs at the same time. The CHPID is spanned across those LCSSs. The use of spanned channels paths decreases the number of channels that are needed in an installation of Z servers. 

A sample of channel paths that are defined as dedicated, shared, and spanned is shown in Figure 5-3. 

<img src='content_image/999829.jpg'>

In the sample, the following definitions of a channel path are shown: 

GLYPH<SM590000> CHPID FF, assigned to PCHID 20A, is dedicated access for partition 15 of LCSS0. The same applies to CHPID 00,01,02 of LCSS0, and CHPID 00,01,FF of LCSS1. 

GLYPH<SM590000> CHPID 03, assigned to PCHID 20E, is shared access for partition 2, and 15 of LCSS0. The same applies to CHPID 05 of LCSS1. 

GLYPH<SM590000> CHPID 06, assigned to PCHID 120 is spanned access for partition 1, 15 of LCSS0, and partition 16, 17 of LCSS1. The same applies to CHPID 04. 

Channel spanning is supported for internal links (HiperSockets and IC links) and for certain types of external links. External links that are supported on z15 servers include FICON Express16SA, FICON Express16S+, FICON Express16S, FICON Express8S, OSA-Express7S, OSA-Express6S, OSA-Express5S, and Coupling Links. 

The definition of LPAR name, MIF image ID, and LPAR ID are used to identify an LPAR by the channel subsystem to identify I/O functions from different LPARs of multiple LCSSs, which support the implementation of these dedicated, shared, and spanned paths. 

