RMS SPD.PDF

RMS Journaling for OpenVMS, Version 6.2, is a software product designed to maintain the data integrity of OpenVMS RMS files and protect them from loss or inconsistency due to various failure scenarios. It offers three primary methods of journaling, which can be applied individually or in combination on a file-by-file basis:

1. After-image (AI) journaling: Allows modifications to a file to be "redone," helping recover lost or corrupted files by restoring them from the latest backup.
2. Before-image (BI) journaling: Enables modifications to a file to be "undone," returning it to a previous known state, useful for correcting erroneous data entries.
3. Recovery unit (RU) journaling: Ensures transaction integrity by treating a group of related operations as "atomic" (all complete or none complete), preventing data inconsistency from incomplete transactions.

The system stores recovery information in "journals," which can be shared by multiple files. RU journaling integrates with DECdtm transaction services, acting as a resource manager to provide atomic operations, including for remote RMS files.

RMS Journaling supports most RMS file organizations (sequential, relative, indexed), with some specific exceptions for certain indexed file types. Both data files and journals must reside on Files-11 Structure Level 2 disks, and journaling across networks or to tape is not supported.

Enabling journaling requires marking files via DCL commands, which typically necessitates exclusive access to the file. While AI and BI journaling require no application changes, RU journaling demands applications to define the start and end of recovery units.

Data recovery processes differ:

• AI/BI recovery is explicit, using the RMS Recovery utility to roll changes forward or backward to a specified time. It relies on a proper backup (made after journaling is enabled and before updates) and requires exclusive file access during recovery.
• RU recovery for incomplete transactions is automatic and transparently handled upon subsequent file access.

The product is fully supported in OpenVMS Cluster environments and can be used with Volume Shadowing to address a broader range of recovery scenarios, such as accidental file deletion, file system corruption, or software errors during multi-block writes. RMS Journaling for OpenVMS Version 6.2 requires OpenVMS Version 6.2.