z/OS V1R6.0 DFSMS Access Method Services for Catalogs

SETCACHE||||||||||||||||||||||||||||||||||||||||||||||||If DASD fast write was active before this procedure was executed, it remains activeafter the procedure completes.1. Before the duplex pair is established, the channel connection address (CCA),which is known to MVS, and the director to device connection (DDC) address,which is the physical address known within the subsystem, are the same aswhen initialized.2. After creating the duplex pair, both addresses directly correlate.3. When SETCACHE SUSPENDPRIMARY is issued, the Storage Control swapsthe CCA-to-DDC assignments between the primary and the secondaryvolumes.4. The system application continues to use the UCB for device 201. However, theStorage Control directs the I/O to the physical device addressed by DDC 12(the target volume). The UCB for the offline device 212 still points to CCA 12,but the Storage Control points CCA 12 to the suspended device (DDC 01).5. When SETCACHE RESETTOSIMPLEX is issued, the Storage Control maintainsthe swapped CCA-to-DDC pointers.Migrating Duplex VolumesThis procedure is valid for migrating a primary or secondary volume in a duplexpair to another like device.vvvvVary the target volume offline to all systems.Issue SETCACHE SUSPENDSECONDARY or SUSPENDPRIMARY, dependingon whether the secondary or the primary, respectively, needs to be taken out ofthe duplex pair.Issue SETCACHE REESTABLISHDUPLEX with the third volume.After the copy completes, perform the required action for the volume suspendedfrom the duplex pair.Note: When you use dual copy to migrate from 3390 devices to RAMAC devices,an invalid format 4 DSCB is created on the target device. Use ICKDSF to fixthe format 4 DSCB. See your IBM representative for the latest service levelof ICKDSF that provides this function.1. When the SETCACHE SUSPENDPRIMARY completes, the system devicenumber points to the CCA address of the old primary volume. Internally, theStorage Control has swapped the CCA-to-DDC pointers. The old primary CCAnow points to the old secondary physical device DDC. Thus, the old secondaryvolume has become the new primary volume; all system I/O is directed to thenew primary. The CCA for the old secondary volume now points to the DDCaddress of the old primary device.2. After the REESTABLISHDUPLEX completes, the new secondary is incorporatedinto the duplex pair, the old primary volume is no longer in the pair, and theCCA of the old secondary now points to the DDC address of the old primary.To run ICKDSF or any other program against the old primary volume, the oldprimary should be addressed as 212.Dual Copy Device Address MappingIn a dual copy environment, normal subsystem activities can modify the internalmapping of the system address (device number) to the actual device. In IDCAMSreports and in the output of the DEVSERV command, the low-order two digits ofthe system address are shown as the CCA, whereas the physical device address isshown as the DDC. The subsystem manages the integrity of this mapping, so itChapter 31. SETCACHE 337