Overview
ISO/IEC 20919:2021 - Information technology - Linear tape file system (LTFS) Format specification - defines the LTFS format requirements for media claiming LTFS compliance. The standard specifies how LTFS structures (the LTFS Label and LTFS Index), data blocks, file marks, partition labels and Medium Auxiliary Memory (MAM) parameters must be arranged so that the data content of an LTFS volume is interchangeable among conformant storage systems. ISO/IEC 20919:2021 is the second edition (2021), adopted from the SNIA LTFS Format Specification (v2.5), and updates interoperability features from the 2016 edition.
Key topics and technical requirements
- Interchangeable data content: Defines the logical layout - size and sequence of data blocks and file marks - required for interoperability among LTFS implementations.
- LTFS Label and LTFS Index: Specifies content and XML formats for the label and index structures that describe files, extents and metadata on tape.
- Partition labels & MAM use: Describes partition labeling and use of drive-specific Medium Auxiliary Memory fields to support metadata like barcodes and vendor tags.
- Index types: Introduces Full and Incremental Indexes to support writing smaller indexes that record only changes since the last index.
- Interoperability features added in 2nd edition: Volume Advisory Locking, Percent Encoding for previously reserved characters in names, File hashes stored in the index, and Open For Write markers for files still open when an index was written.
- Scope limits: The standard governs logical format and interchangeability of data content - it does not include tape command sequences or low-level drive control instructions.
- Compatibility note: Physical media interchange also depends on physical media and drive compatibility (e.g., tape cartridge and drive family).
Practical applications
- Long-term archival and backup where file-level access is needed on tape (e.g., media asset management, cold storage, regulatory archives).
- Tape-based data migration between vendors and platforms while maintaining file metadata and integrity.
- Implementations of LTFS-capable software, tape libraries and archiving appliances that require a defined interchange format for portability and auditability.
- Use cases requiring incremental index updates, file integrity verification (file hashes), and safe-volume locking for managed media pools.
Who should use this standard
- Storage architects, backup/archival engineers and system integrators implementing LTFS on tape libraries.
- Software developers building LTFS writers/readers, file-system interfaces, or media-management tools.
- Archive and media asset professionals requiring interoperable tape formats for long-term retention.
Related standards
- ISO/IEC directives and JTC 1 procedures for standard development.
- Tape technology and drive-family specifications (for physical-media compatibility), and SNIA LTFS technical materials referenced by the specification.
Keywords: ISO/IEC 20919:2021, LTFS, Linear Tape File System, LTFS Label, LTFS Index, MAM, tape archival, tape interoperability, incremental index, volume advisory locking.