RDF/IMP, IMPX, and ZLT System Management Manual

Introducing RDF
HP NonStop RDF/IMP, IMPX, and ZLT System Management Manual—524388-002
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RDF Subsystem Overview
There are three versions of the RDF product:
1. RDF/IMP (product number T0346) provides online product initialization, online
database synchronization, triple contingency support, subvolume- and file-level
replication, stop-update-to-time (for quiescing the backup database to a stable
state), NonStop SQL/MP big files support, and many other features.
2. RDF/IMPX (product numbers T0346 and T0347) provides the same functionality
as RDF/IMP, but also replication of auxiliary audit trails, support for network
transactions, and lockstep operation.
3. RDF/ZLT (product number T0618) provides zero lost transaction (ZLT) protection
using mirrored disks.
RDF/IMP and IMPX run on either K-series or S-series systems. The ZLT functionality
is only available on S-series hardware, although RDF/ZLT runs correctly on K-series
systems without using ZLT protection.
Before reading further in this manual, you should be familiar with the concepts,
terminology, and functions of the NonStop TMF product. You should know about the
objects on which TMF operates, such as transactions, audit trails, and audit volumes.
You should understand how TMF software uses elements like before-images, after-
images, and control records. In addition, you should also understand the TMF
processes that perform backout, volume recovery, and file recovery. If you are not
familiar with this information, you should read the Introduction to the HP NonStop
Transaction Management Facility (TMF).
RDF Subsystem Overview
RDF maintains a logically replicated database on one or more backup systems by
monitoring changes made to audited tables and files on designated primary system
volumes and applying those changes to corresponding volumes on the backup system.
Although logically the same as the primary database, a backup database is not an
actual physical copy. For those volumes designated to be protected by RDF, the
backup database contains the same data for all committed transactions as in the
primary database.
On the primary system, RDF extractor processes read audit trails (logs maintained by
TMF of all database transactions that affect audited tables and files), and send all audit
information associated with volumes protected by RDF to RDF receiver processes on
the backup system. Each receiver process sorts the audit information and writes it to
the appropriate image trail. RDF updater processes on the backup system read their
image trails and apply the changes to the backup database. An RDF purger process
on the backup system interacts with the updaters to determine when image files can be
purged.
Each volume protected by RDF on the primary system has its own updater process on
the backup system responsible for applying audit information to the corresponding
volume on the backup system.