IBM Z9, Planning Manual

Page: 174 / 274

Defining Shared Channel Paths
Before defining shared channel paths, consider the following:
v Only CTC, CNC, CBP, CFP, CIB, ICP, OSC, OSD, OSE, OSN, FC, FCV, FCP,
and IQD channel paths can be shared. CVC and CBY channel paths cannot be
shared. On CF only models, CBP, CFP, and ICP channel paths cannot be
shared.
v 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.
v
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 nonreconfigurable channel path. Only one LP can
access I/O devices on this channel path.
You cannot mix unshared and shared CHPIDs to a device.
Channel Path Access and Candidate Lists
If a channel path is either shared or reconfigurable, you can specify which LPs have
access to that channel path. Use the channel path access list with or without the
channel path candidate list.
Channel Path Access List
An LP has initial access to a channel path if the LP is on that
channel path’s access list.
For the first power-on reset with an LPAR IOCDS, the access list
defines which LPs will initially have the channel path configured
online. Reconfigurable and shared CHPIDs may later be accessed
by LPs not in the access list. Subsequent power-on resets with the
same LPAR IOCDS will have any reconfigurations applied and the
LPs may have access to channel paths other than those that were
specified in the initial access lists for the channel paths. See
“Channel Path Reconfiguration and Logical Partition Activation” on
page 3-53 for more information on assigning channel paths to an
LP.
Channel Path Candidate List
An LP can gain access to a channel path if the LP is on that
channel path’s candidate list. An LP is allowed to configure a
channel path online if the LP is in that channel path’s candidate list.
3-48
PR/SM Planning Guide
|