Availability Guide for Application Design

Data Protection and Recovery
Availability Guide for Application Design—525637-004
4-13
Using the Remote Duplicate Database Facility (RDF)
Products
Using the Remote Duplicate Database Facility (RDF) Products
HP provides for site-level or environmental fault tolerance with the NonStop RDF (K-
series only), NonStop RDF/MP, and NonStop RDF/MPX products. Each RDF product is
an online database utility that can help speed the process of getting an application up
and running at a backup site when its primary site suffers a complete disaster such as
fire, flood, or earthquake.
Figure 4-3 on page 4-13 shows a system in Chicago being used to provide disaster
backup for applications running on a system located in Boston that normally provides
services to a network of users.
The RDF product maintains the backup site’s database in the following way. RDF
sends the after-image audit records of complete transactions over the network to the
remote backup system. The audit records are applied to the backup system’s copy of
the application database. If disaster strikes, the backup system has enough information
to ensure that it can take over application processing against an up-to-date copy of the
database.
RDF can be incorporated into an application without any change to the application
code. Its cost, in addition to the extra hardware, includes two periods of downtime: the
Figure 4-3. An RDF Product Provides Protection Against Site Failure
Server
Boston
$DBBO
$AUDIT
Chicago
RDF
$IMAGEBO
$DBBO
Server
RDF
Normal
Information
Flow
Flow if
Primary
Down
Network
VST303.vdd