Accessing secondary volumes while XRC is active

Applications can read secondary volumes while XRC continues to copy data to these volumes. However, you should consider the following when accessing secondary volumes from another system:

The secondary volume serial number is different than the primary volume serial number. Access to the secondary volume must be by a different catalog or by explicit unit, volume, and serial number reference.
Whenever the VTOC location on a volume changes, the new location must be updated in an in-storage pointer to the VTOC. XRC performs this refresh on the SDM system whenever it copies the primary volume VTOC pointer to the secondary volume. To refresh the pointer on other systems attached to the secondary volume, issue the console commands to vary the secondary volume offline and then online. Failure to do this can result in I/O errors when attempting to access the old VTOC.
XRC continuously copies application updates to a secondary volume that remains in the XRC session. A program that reads from the secondary volume must be able to manage the fact that the data continues to change.
Note: VSAM volume data set (VVDS) information will reflect the primary volume, not the secondary volume.

Error conditions can occur during reads, however, due to the way that XRC handles secondary I/O functions. An example of this is an I/O error that results when the VTOC is updated before XRC has completely copied the data to the secondary volume. Applications that access secondary XRC volumes must be able to handle these temporary error situations. You can often resend the read I/O to clear these errors.