IBM SC34-7012-01 manual summarizes the tier 6 solution

Figure 24 summarizes the tier 6 solution.

Site One Site Two

VTAM

3745 3745

Channel extender

ESCON

39903990

Approach	Recovery
Local and remote copies	Most expensive
updated	Instantaneous recovery
Dual online storage	Non-disruptive terminal switch
Network switching capability

Figure 24. Disaster recovery tier 6: minimal to zero data loss

Tier 6, minimal to zero data loss, is the ultimate level of disaster recovery.

There are two tier 6 solutions, one hardware-based and the other software-based. For details of the hardware and software available for these solutions, see “Peer-to-peer remote copy (PPRC) and extended remote copy (XRC)” on page 234 (hardware) and “Remote Recovery Data Facility” on page 236 (software).

The hardware solution involves the use of IBM 3990-6 DASD controllers with remote and local copies of vital data. There are two flavors of the hardware solution: (1) peer-to-peer remote copy (PPRC), and (2) extended remote copy (XRC).

The software solution involves the use of Remote Recovery Data Facility (RRDF). RRDF applies to data sets managed by CICS file control and to the DB2, IMS, IDMS, CPCS, ADABAS, and SuperMICR database management systems, collecting real-time log and journal data from them. RRDF is supplied by E-Net Corporation and is available from IBM as part of the IBM Cooperative Software Program.

The benefits of tier 6 are:

vNo loss of data.

vRecovery in a very short period of time.

vEmergency restart at remote site should be possible.

The drawbacks are the cost of running two sites and the communication overhead. If you are using the hardware solution based on 3990-6 controllers, you are limited in how far away your recovery site can be. If you use PPRC, updates are sent from the primary 3990-6 directly to the 3990-6 at your recovery site using enterprise systems connection (ESCON®) links between the two 3990-6 devices. The 3990-6 devices can be up to 43 km (26.7 miles) apart subject to quotation.

If you use XRC, the 3990-6 devices at the primary and recovery sites can be attached to the XRC DFSMS/MVS host at up to 43 km (26.7 miles) using ESCON links (subject to quotation). If you use three sites, one for the primary 3990, one to

232CICS TS for z/OS 4.1: Recovery and Restart Guide