between the primary and secondary sites is interrupted. Remote logging is only as effective as the currency of the data that is sent off-site. RRDF transports log stream data to a remote location in real-time, within seconds of the log operation at the primary site.

When the RRDF address space at the remote site receives the log data, it formats it into archived log data sets. Once data has been stored at the remote site, you can use it as needed to meet business requirements. The recovery process uses standard recovery utilities. For most data formats, first use the log data transmitted by RRDF in conjunction with a recent image copy of the data sets and databases that you have to recover. Then perform a forward recovery. If you are using DB2, you have the option of applying log records to the remote copies of your databases as RRDF receives the log records.

If you use DB2, you can use the optional RRDF log apply feature. With this feature you can maintain a logically consistent “shadow” copy of a DB2 database at the remote site. The RRDF log apply feature updates the shadow database at selected intervals, using log data transmitted from the primary site. Thus restart time is shortened because the work needed after a disaster is minimal. The currency of the data depends on the log data transmitted by RRDF and on how frequently you run the RRDF log apply feature. The RRDF log apply feature also enhances data availability, as you have read access to the shadow copy through a remote site DB2 subsystem. RRDF supports DB2 remote logging for all environments, including TSO, IMS, CICS, batch, and call attach.

At least two RRDF licenses are required to support the remote site recovery function, one for the primary site and one for the remote site. For details of RRDF support needed for the CICS Transaction Server, see “Remote Recovery Data Facility support” on page 239.

Choosing between RRDF and 3990-6 solutions

About this task

Table 3 summarizes the characteristics of the products you can use to implement a tier 6 solution. You must decide which solution or solutions is most appropriate for your environment.

Table 3. Selecting a tier 6 implementation. This table compares the strengths of the tier 6 solutions.

 

RRDF

3990-6

 

 

 

Data type supported

Various data sets1

Any on DASD

Database shadowing

Optional. Available for DB2

Optional

 

and IDMS only

 

 

 

 

Forward recovery required

Yes

Depends on implementation

 

 

 

Distance limitation

None

About 40 km for ESCON.

 

 

Unlimited for XRC with

 

 

channel extenders

 

 

 

Note: 1 Data sets managed by CICS file control and the DB2, IMS, IDMS, CPCS, ADABAS, and SuperMICR database management systems.

Disaster recovery personnel considerations

When planning for disaster recovery, you need to consider personnel issues.

Chapter 19. Disaster recovery 237

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IBM SC34-7012-01 manual Choosing between Rrdf and 3990-6 solutions, Disaster recovery personnel considerations