Resolving duplicate device number conflicts

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Consider options A, B, and C when planning the I/O configuration and the reconfigurability of channel paths. You can resolve duplicate device number conflicts by choosing one of the options:

A
Use the original channel path:

If the receiving logical partition does not need a new path to a shared device or does not need the new (unshared) device, take no action. The conflict is resolved by using only the original path (shared device) or the original device. (Access is still allowed to any non-conflicting devices on the newly configured channel path.)

In Figure 1 , ZOSTEST can access device 180 only through channel path 10 if the operator takes no action in response to the conflict message.

B
Deconfigure the original channel path:

If the logical partition must have the reassigned channel path to a shared device or access to a new (unshared) device, the conflict is resolved by substituting the reassigned channel path for the original channel path. Do the following:

  1. Configure offline the original channel path (CHP 10 in Figure 1 ).
  2. Configure offline and then online the reassigned channel path (CHP 04 in Figure 1).
  3. If necessary, configure online the original channel path (CHP 10 in Figure 1). Another conflict message is issued because a new conflict has been created. The operator then ignores this conflict as described in option A. (Access is still allowed to any non-conflicting devices on the original channel path.)

In Figure 1, ZOSTEST can access device 180 only through channel path 04 if the preceding steps are performed in response to the conflict message.

C
Change the I/O configuration:

Only option C provides a permanent resolution to a device number conflict.

If the logical partition must have access to all devices over the original channel path and the reassigned channel path (shared devices), or to a new device and the original device (unshared devices), do one of the following:

  • Create a configuration with unique device numbers, if they are unshared devices.
  • For shared devices, define a single device with access to all the channel paths attached to the physical control units.
  • For a shared device assigned to unshared channel paths, change the channel paths to shared and consolidate the control units and device definitions to one each.
  • If the device is assigned to shared channel paths, control access to the devices using their device candidate list.

The configuration can be activated by performing a POR or by performing a dynamic I/O configuration.

In Figure 1 (shared device), ZOSTEST can access device 180 through CHP 04 and CHP 10 if CHP 04 is defined to ZOSTEST in the IOCDS.

In Figure 1 (unshared device), ZOSTEST can access either device 180 (unshared device) if one or both of the devices are assigned a new device number in the IOCDS.

When a device number conflict exists, logical partitions fail to activate. This happens when one of the following conditions occurs:

  • The receiving logical partition was deactivated when a channel path is reassigned
  • The receiving logical partition is deactivated after a channel path is reassigned

Failure to activate can result if options A or B are used. If a logical partition fails to activate, use option B or C to resolve the conflict and to activate the logical partition.

In Figure 1, if ZOSTEST is not active when CHP 04 is reassigned, or ZOSTEST is deactivated and then activated after CHP 04 is reassigned, ZOSTEST does not activate until the conflict over device 180 is resolved.

If you resolve the conflict by using option B do the following steps:

  1. Establish the correct configuration by configuring offline one of the channel paths (CHP 04 or CHP 10)
  2. Configure offline and then online the other channel path

If it is necessary to have access to other devices on the first channel path, the operator can configure online the first channel path while the LP is active. Ignore the messages issued at the hardware console.

The following IOCP statement example shows coding that removes duplicate device number conflicts for shared devices.

CHPID PATH=(00),PARTITION=(ZOSPROD,REC), . . .
CHPID PATH=(04),PARTITION=(ZOSPROD,REC), . . .
CHPID PATH=(10),PARTITION=(ZOSTEST), . . .
CNTLUNIT CUNUMBR=0001,PATH=(00,04),UNITADD=80
CNTLUNIT CUNUMBR=0002,PATH=(10),UNITADD=80
IODEVICE ADDRESS=180,CUNUMBR=(0001,0002)