Linear Tape-Open

Start with three separate questions: which cartridge fits the reader, how many uncompressed bytes it holds, and how the application finds those bytes. LTO answers the media-format question; LTFS answers a file-format question; the backup policy must answer where another usable copy lives.

The LTO Program lists 18 TB native for LTO-9 and 30 TB or 40 TB for LTO-10. Both generation pages list up to 400 MB/s native streaming. At the same rate, greater capacity takes longer to transfer in full; it does not reduce the time needed for a fixed amount of data. These are published specifications, not measurements of a particular workload. Drive model, host path and tape positioning affect achieved performance.

LTFS makes files visible through a directory tree, but does not turn tape into a disk. IBM's documented layout writes indexes in both partitions. The index partition can also hold selected file data under a placement policy; it is not restricted to metadata. The data partition contains indexes as well as payload. The partition names describe their roles, not an absolute separation of contents.

The original MSST 2010 paper by Pease and colleagues separates file-interface convenience from physical access time. Its LTO-5 experiment used 175 GiB of zero-filled data and sampled 100 random first-byte reads, reporting mean seek times around 37 seconds. That is one historical setup, not a current latency forecast or a tail-latency bound. A familiar file browser does not eliminate tape positioning.

Updating a file is also different from overwriting disk sectors. IBM Storage Archive LE appends replacement data and changes the index references. Ordinary deletion removes a file entry without reclaiming its recorded space. A deleted name therefore does not establish secure erasure. Treat disposal and sanitization as a separate procedure.

Rollback selects an available earlier index generation. IBM Storage Archive's erase-history option makes later generations unavailable for recovery; a rollback that preserves history has different consequences. Record the implementation and chosen mode before recovery work, and do not assume that a repair or rollback operation is read-only.

Recovery compatibility is narrower than mount compatibility. SNIA LTFS 2.5.1 requires full indexes at clean unmount, but permits intermediate incremental indexes. Annex H warns that older recovery software may fail or discard newer changes on an inconsistent volume if it cannot interpret those increments. Check the recovery tool's format support, not just whether it can mount a clean cartridge.

Engineering implication: duplicate indexes on one cartridge are metadata-recovery aids, not independent file backups. IBM Spectrum Archive EE documents payload replication into separate tape pools as a distinct operation. Plan independent copies and restore checks around the data, its catalog, compatible readers and any required encryption keys.