OpenVMS Guide to Extended File Specifications

This document, "OpenVMS Guide to Extended File Specifications," outlines the features, benefits, and considerations for implementing Extended File Specifications (EFS) on OpenVMS Version 7.2 Alpha systems.

Key Features of Extended File Specifications:

1. ODS-5 Volume Structure:

   • Long File Names: Allows file names (excluding version) up to 236 8-bit or 118 16-bit characters. Full file specifications exceeding 255 bytes are abbreviated by RMS for unmodified applications.
   • Expanded Character Set: Supports ISO Latin-1 and 16-bit Unicode (UCS-2) characters. Certain special characters (e.g., ",*,:,<,>,/,?,|,) are excluded or require an escape character (^) for literal interpretation.
   • Case Preservation: File names retain their original case, unlike previous OpenVMS versions which converted to uppercase.

2. Deep Directory Structures: Supports up to 255 levels of nested directories, a significant increase from prior versions.

Benefits:

• Improved compatibility and transparency for users in Windows 95/98/NT environments, particularly for Advanced Server for OpenVMS (formerly PATHWORKS), DCOM, and JAVA applications.
• Enables OpenVMS system managers and users to utilize longer, mixed-case, and internationalized file names with deeper directory paths.

Implementation Considerations & Management:

• System Compatibility: Compaq strongly recommends enabling ODS-5 volumes only on homogeneous OpenVMS Alpha Version 7.2 clusters. Older OpenVMS versions (pre-7.2) cannot mount ODS-5 volumes, and VAX systems have limited functionality, often displaying "pseudonames" for non-ODS-2 compliant files.
• Enabling ODS-5: New volumes can be initialized using INITIALIZE /STRUCTURE_LEVEL=5. Existing ODS-2 volumes can be converted to ODS-5 using SET VOLUME /STRUCTURE_LEVEL=5 (a backup is crucial as direct conversion back to ODS-2 is not supported).
• Converting ODS-5 to ODS-2: Possible through BACKUP operations using the /CONVERT qualifier, which converts ODS-5 names to ODS-2 compliant names (with potential loss of ODS-5 attributes).
• Access Control: System managers can restrict access to ODS-5 volumes for VAX users or untested applications using OpenVMS discretionary controls (e.g., Access Control Entries and identifiers).
• DCL Support: By default, DCL uses a TRADITIONAL (ODS-2) parsing style. To fully utilize EFS on Alpha systems, users must activate SET PROCESS/PARSE_STYLE=EXTENDED. Modified DCL commands (like DIRECTORY, TYPE, DELETE, PURGE) offer a /STYLE=(CONDENSED,EXPANDED) qualifier to control how extended file names are displayed.
• Utility Changes: Key system utilities such as ANALYZE/DISK_STRUCTURE, BACKUP, and MOUNT have been enhanced to support EFS.

Application Development Considerations:

• Support Levels: Applications can have full, default, no EFS, or no ODS-5 support. Most unmodified applications fall into "Default Support," which may involve RMS abbreviating long file names and potential case-sensitivity issues.
• Required Modifications: Applications using undocumented interfaces, direct physical I/O, or making assumptions about file system internal structures, file name syntax, case, or directory depth will likely require modifications.
• Upgrading for Full Support: Involves transitioning from traditional NAM (Name Access Block) structures to the new NAML (Long Name Access Block) for file specifications over 255 bytes, expanding buffer sizes, and using specific flags (e.g., LIB$M_FIL_LONG_NAMES, FDL$V_LONG_NAMES).

The document stresses the importance of thorough review, testing, and understanding compatibility implications before enabling ODS-5 in an OpenVMS environment.