RMS SPD.PDF

This document describes RMS Journaling for OpenVMS, Version 7.0, a software product designed to maintain data integrity and protect OpenVMS RMS files from loss or inconsistency due to various system failures. It applies to both OpenVMS VAX and Alpha architectures.

Key features and methods include:

1. After-Image (AI) Journaling: Allows "redo" operations, recovering lost or corrupted files by applying recorded modifications to the latest backup copy.
2. Before-Image (BI) Journaling: Allows "undo" operations, reverting files to a previous known state, particularly useful for correcting erroneous data.
3. Recovery Unit (RU) Journaling: Ensures transaction integrity for "atomic" groups of operations, preventing data inconsistency from incomplete transactions. It integrates with DECdtm transaction services.

Journaling is enabled on a file-by-file basis using the DCL SET FILE command, requiring exclusive access during marking. While AI/BI journaling requires no application changes after marking (just reopening files), RU journaling necessitates application modifications to define recovery units. Journaled files and journals must reside on Files-11 On-Disk Structure 2 (ODS-2) disks, and journaling is not supported across networks or to tape.

Data Recovery:

• AI/BI Journaling: Uses the RMS Recovery utility for explicit, file-by-file rollback or roll-forward to a user-specified time, requiring a backup made with the BACKUP utility.
• RU Journaling: Automatically rolls back incomplete transactions upon the next file access, requiring no user intervention.

Interactions and Limitations:

• Can be used with Volume Shadowing, providing additional recovery for issues like mistaken deletions or file system pointer corruption.
• RU journaling alone cannot recover from multiblock bucket write corruption in indexed files; a combination with AI journaling is needed for these scenarios (e.g., host failures, disk path loss).
• AI and BI journals require periodic maintenance, which may necessitate stopping applications.

Requirements:

• Requires OpenVMS Version 7.0.
• Fully supported in VMScluster environments.
• Distributed and installed as a System Integrated Product with OpenVMS V7.0.
• Licensed on a capacity (per CPU) basis.