Compatibility and Interoperability
Scope
This domain tests the generation rules, media-type exceptions, WORM and encryption interchange, and what "interchange" actually guarantees across drives, libraries and software.
Core rules
- Read two back, write one back. A drive writes its own generation and the previous one, and reads its own, the previous one, and the one before that. LTO-9 writes LTO-8/LTO-9 and reads LTO-7/LTO-8/LTO-9. LTO-8 reads LTO-6 and writes LTO-7 (including M8) and LTO-8.
- Interchange means a compliant cartridge written on any compliant drive of a generation is readable on another compliant drive within the compatibility window. The format, not the vendor, defines it.
- WORM (LTO-3 onward) cartridges cannot be re-initialised or overwritten; data can only be appended past the last end-of-data. Immutability is enforced by drive and cartridge identity, not by a software policy flag.
- Encryption is drive-level from LTO-4 (AES-256-GCM). An encrypted tape is readable wherever the media is readable, provided the drive is encryption-capable and the key manager returns the correct key.
- Mixed libraries work because generation and media type are read from LTO-CM and the barcode label before any mount. Software must still zone media pools so a mislabelled cartridge never lands in an incompatible drive.
Worked example
A library holds LTO-6, LTO-7, LTO-8 and LTO-9 drives, plus LTO-6, LTO-7 MP, LTO-7 M8 and LTO-8 media. Route LTO-6 media to LTO-6/LTO-7/LTO-8 drives only - an LTO-9 drive cannot read it; route M8 media to LTO-8 drives only; LTO-7 MP can go to LTO-7, LTO-8 or LTO-9 drives.
Traps
- Reading "backward compatible" as "all previous generations".
- Assuming WORM alone satisfies retention: it stops overwriting, but you still need key custody and a catalog to find the file.
- Forgetting that a mixed fleet needs both a compatible drive and a compatible software generation.