Types of backups needed for a recovery
Before performing a recovery, you must verify that all the data has been backed up or archived and registered in the RUV repository. This topic describes the types of backups and how RUV uses the different backups for a good recovery.
In the simplest terms, before you can perform a recovery you must have a valid backup of the VSAM files and all the changes that were made to the file since the backup was performed. This topic assumes that the backup and recovery are performed on the local system; however, the principles also apply to remote recovery and disaster recovery operations.
Crisp backup
In an ideal backup situation (which is rare), all transactions are paused while a backup is made. The following figure shows this ideal situation:
Prior to a backup point, multiple transactions (T1, T2, and so on) are processed by CICS, and the DFHLOG collects the log stream information about each transaction. At the backup point, all transaction activity pauses while a backup is made. When the backup is completed, the processing of transactions resumes. Few organizations can afford to bring their operations to a stop while they do a crisp backup.
Fuzzy backup
A more realistic backup situation is shown in the following figure:
During the time that the backup is being made, CICS continues processing transactions. This fuzzy backup contains both completed transactions (T1 and T2) and partially completed (in-flight) transactions (T3 and T4). During the time of the backup, the log stream (DFHLOG) continues to record all transaction activities in a time sequence.
RUV allows you to specify a fuzzy backup using the Backup-While-Open (BWO) feature. This is especially important to operations that require system and application availability 24 hours a day, 7 days a week. A recovery must be run against the data set when a fuzzy backup is restored.
Recognized backup formats
RUV can generate fuzzy backups of VSAM data sets and use these backups and archives for recovery. RUV also recognizes SMS backups. During a recovery, RUV automatically checks for SMS backups and uses the more current SMS or RUV backup.
RUV also supports alternate backup techniques and can restore the resulting backup files (called external backups) automatically in a recovery situation. To use external backups, you must provide required information in a one-time definition process.