The storage administrator must identify the application volumes to copy, and create extended remote copy volume pairs. XRC provides an image copy of a volume on a record-for-record basis. There is a one-to-one correspondence between the record on the primary volume track and the record on the secondary volume track. Because the data written on the primary disk is written to the same tracks on the secondary disk, the secondary disk must have the same track size and number of tracks per cylinder, and the same or larger volume capacity, as the primary. (If these criteria are not met, the XADDPAIR command will fail.) Ensure that secondary volumes are part of a storage group that does not allow allocations, and dedicate these volumes to XRC use only.
Remote copy supports volumes, not data sets. As a result, all data sets on the volumes that are copied are part of remote copy activity, and are therefore copied to the target volume. This support is application (IBM® or non-IBM) independent, and supports all data set types.
Because applications deal with data sets and not volumes, multivolume data sets require special attention. Multivolume data set types include data sets that reside on multiple volumes, striped data sets, and VSAM spheres. Unless you copy all volumes of a multivolume data set, XRC will copy only part of the data set. Other data sets on the copied volume may be usable, but the multivolume data sets will not be. If multivolume data sets are critical for recovery, you must copy all volumes on which these data sets reside. In addition, if these data sets are critical to the system, start the XRC session by issuing the XSTART or XADDPAIR command with the ERRORLEVEL(SESSION) or (group_name) parameter specified.
In the event of an error, specifying ERRORLEVEL(SESSION) ensures data consistency across all volume pairs in the entire XRC session. Specifying ERRORLEVEL(group_name) ensures that data is consistent across all volume pairs that belong to the specified group. Errors within the specified group do not affect the update activity of volume pairs that belong to other groups.
If the data sets require consistency as a group, issue the XADDPAIR command for these related data sets. Specify the ERRORLEVEL parameter with a group name that is meaningful for the related volumes. Specified as such, an error for one volume pair would suspend the entire set of volumes that are associated with the named group. After correcting the error, you can add the volume group back to the XRC session.
For additional information about the XADDPAIR command, refer to XADDPAIR–Adding volume pairs or utility volumes.
For additional information about the ERRORLEVEL parameter, refer to Recovering from error conditions using extended remote copy.