IBM SC34-7012-01 - Manual (Page 244)

Figure 24 summarizes the tier 6 solution.
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:
v No loss of data.
v Recovery in a very short period of time.
v Emergency 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
Approach Recovery
Most expensive
Instantaneous recovery
Non-disruptive terminal switch
Site Two Site One
VTAM
Channel extender
3745 3745
3990 3990
ESCON
Local and remote copies
updated
Dual online storage
Network switching capability
Figure 24. Disaster recovery tier 6: minimal to zero data loss
232 CICS TS for z/OS 4.1: Recovery and Restart Guide