Steps for using P/DAS in a nonsysplex, shared-disk environment

This topic describes the sequence of commands for performing a P/DAS operation in a nonsysplex, shared-disk environment. In all cases, device ssss refers to the primary source volume. Device tttt refers to the secondary target volume.

Before you begin:

Identify all systems that have access to the devices that you want to switch. You must issue the commands that follow on all systems that are connected to the devices that you plan to switch.
If volume pairs are in PPRC extended distance mode, convert the pairs to synchronous mode to allow them to reach DUPLEX status before a swap operation begins. This ensures that the volume pairs are in sync and all updates are copied to the secondary.

Perform the following steps to use P/DAS in a nonsysplex, shared-disk environment:

Issue IOACTION STOP,DEV=ssss.
Initiate a P/DAS operation by issuing an IOACTION STOP command on all systems that are attached to the primary volume that is specified by DEV=ssss. This command requests that P/DAS stop I/O that is directed to device number ssss. DEV=ssss specifies a primary volume of a duplex PPRC volume pair.

All application I/O that is issued to the primary volume remains queued in the MVS system until you issue an IOACTION RESUME command. P/DAS ends, with a simulated I/O error, any active I/O that does not complete within five seconds after the MVS system has accepted the IOACTION STOP. This action forces the disk error recovery procedures to retry the I/O operation.
The MVS system issues the following messages to the operator console (or consoles) of all systems when the I/O for the primary device has been stopped on that system:
```
 IOS600I IOACTION - THE FOLLOWING DEVICE(S) HAVE BEEN STOPPED:
                   dev dev1-dev2...
 
   IOS601I IOACTION - DEVICES REMAIN IN THE STOPPED STATE.
           USE THE 'D IOS,STOP' COMMAND TO DISPLAY THE DEVICES
```
When all attached systems have received the above messages, issue the swap command to switch volumes. MVS issues an IOS610I message in response to your D IOS,STOP command.
Issue SWAP ssss,tttt.
Issue the SWAP command for the volume pairs involved in the P/DAS operation. The SWAP command directs the system to switch the source device ssss with the target device tttt and prepares the system to redirect all I/Os issued to device ssss to the target device tttt. Issue this command on all systems that are attached to the volumes that you plan to switch.

Note: Be aware that swapping between devices that are not a PPRC volume pair is currently allowed. However, because these devices are not a PPRC volume pair, there is no guarantee that the data on both volumes match. If the swap is allowed to continue based on the reply to message (IGF523A) by the operator and the volumes do not match, the data that is yet to be copied will be lost.
If I/O cannot be issued to the primary device of a volume pair being swapped, then the swap will not proceed even if the operator indicates for the swap to continue. I/O access to the primary and secondary volumes of the swapping pair is required.
P/DAS performs validation.
Before the SWAP operation is complete, P/DAS performs validation to ensure that it can complete the swap operation. If conditions exist that can cause a data integrity exposure, P/DAS ends the operation and generates an error message. See P/DAS error conditions for error message descriptions.

P/DAS does not proceed when it cannot determine the status of both volumes, or when the volumes are not in duplex state. Ensure that the environment meets the conditions necessary to support P/DAS. Preparing for P/DAS operations describes the conditions.
If the validation completes successfully, P/DAS issues the following message to prompt the operator as to how to proceed:
```
IGF520A VERIFICATION COMPLETE: REPLY 1 TERMINATE PAIR, AND SWAP
    │ 2 SWITCH PAIR, AND SWAP │ 3 CONTINUE SWAP │ 4 TERMINATE SWAP
```
Reply to the IGF520A message.
Replying to P/DAS-related messages describes message reply options. The system takes action according to two things:
- The option that is selected by the operator
- The environment that exists at the time the command is issued.
The system issues the following completion message after the swap function is complete:
```
IGF505I SWAP FROM ssss TO tttt COMPLETE
```
Variable ssss is the source device number, and tttt is the target device number.
Issue IOACTION RESUME,DEV=tttt.
In a shared-disk environment, ensure that all attached systems have received the IGF505I message before you issue the IOACTION RESUME command. After you have received the IGF505I message, issue an IOACTION RESUME command from all systems that are attached to device tttt. You must issue the command to device number tttt because device tttt is now the primary volume. The IOACTION RESUME command resumes all application I/O to device tttt. All application I/O that used to go to the source device ssss now goes to the target device tttt instead. This includes all I/O that is queued by MVS since the STOP command and all subsequent I/O. You must issue this command on all systems that share this volume.
The following message received at the console indicates that all application I/O has resumed and that the P/DAS operation has completed:
```
IOS607I IOACTION - THE FOLLOWING DEVICE(S) HAVE BEEN RESUMED:
                    dev,dev1-dev2 
```