TMF Introduction (G06.26+)

Transaction Protection and Database Recovery
HP NonStop TMF Introduction—522414-002
3-13
File Recovery
Online dumps of database files can be initiated manually through the TMFCOM
interactive command interface to TMF. Alternatively, they can be started
programmatically through the Subsystem Programmatic Interface (SPI). Using SPI,
these subsystem management programs are ideal for controlling online dumps at
unattended sites. Sites can also manage dumps by using HP Tandem Advanced
Command Language (TACL) programs.
The online dump process can write duplicate, simultaneous dumps: the business can
then keep one or more sets of storage media off site for protection if a fire or other
disaster damages an installation.
A site should store online dumps for possible future use. A site that does not dump
and preserve audited files will not be able to perform file recovery.
Online dumps are recorded in the TMF catalog and are managed automatically by
TMF; the TMP purges dump files as they are no longer needed for recovery
operations.
File Recovery
If a system or media failure jeopardizes the consistency of one or more audited files,
those files cannot be opened again until they have been recovered. Although volume
recovery can recover a database in most situations, file recovery is needed to restore
consistency to the database after a critical failure has occurred. A critical failure can
take place when:
•
A disk has become corrupted.
•
A system failure has occurred from which volume recovery cannot recover.
•
An audited file or volume is affected by a failure of a nonmirrored volume or both
disks of a mirrored volume.
•
An application incorrectly updates a database. If online dumps of the affected files
exist from before the application problem, file recovery can recover the files to a
state prior to the incorrect updates.
•
A file is accidentally purged.
File recovery uses online dumps of database files and audit dumps to restore damaged
files, as shown in Figure 3-7.