Channel configuration considerations

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The following configuration rules determine how logical paths are established for FICON® channels.

  • A channel initially attempts to establish logical paths:
    • If you perform POR, only those channels configured online to LPs that are activated and IPD'ed at POR may attempt to establish logical paths. Shared channels attempt to establish logical paths only for those activated and IPL'ed LPs with the channel configured online when the operating system drives the first I/O operation to a device on a logical control unit accessed through that channel.
    • When the LP is activated and IPD'ed and the operating system drives the first I/O operation to a device on a logical control unit accessed through that channel.
    • When the channel is configured online (if previously configured offline) and the operating system drives the first I/O operation to a device on a logical control accessed through that channel.
  • A channel cannot establish a logical path or has its logical path removed when:
    • An LP is deactivated. A shared channel continues to operate for any other remaining activated LPs to which it is defined. Logical paths to those LPs remain established.
  • A shared channel cannot establish a logical path to a control unit for an LP that cannot access any of the I/O devices on the control unit. In IOCP, the PARTITION or NOTPART keyword on the IODEVICE statement specifies which LPs can access a device.
  • A channel that cannot initially establish a logical path can reattempt to establish a logical path if the channel detects or is notified of one of the following conditions and informs the operating system of the condition resulting in the operating system driving an I/O operation to a device on a defined control unit:
    • A change in the state of a control unit
    • A change in the state of a link or port
    • A dynamic I/O configuration change that frees previously allocated logical paths
  • A channel cannot establish a logical path or has its logical path removed if:
    • The Director that connects the channel to the control unit blocks either the channel port or control unit port used in the path.
    • The Director that connects the channel to the control unit prohibits the dynamic connection or communication between the channel port and the control unit port used in the path.
    • A link involved in the path fails or is disconnected. When a shared channel is affected by a port being blocked, a dynamic connection or communication being prohibited, or a link failing or being disconnected, each LP sharing the channel is equally affected and all logical paths using the port or link (regardless of which LP they are associated) are removed.
    • The channel is configured offline. When a shared channel is configured offline for an LP, it continues to operate for any other LP that has the channel configured online. Logical paths to these other logical partitions remain established.
    • Power to the channel, control units, or Directors in the configuration is turned off.