Preservation
A chain, therefore a weakest link
A preservation workflow is the sequence of stages that takes an image from the memory card to a state where it will remain readable and understandable over time. What makes it a chain, rather than a list of tips, is that a missing stage cancels the others.
Perfect checksums on a collection with no descriptive metadata: you’ll know you are faithfully preserving images nobody can identify. Impeccable metadata with no off-site copy: the description disappears with the building.
The six stages
- Ingest. Copy from the card, verifying the copy is faithful before erasing the source. It’s the only moment the original still exists in duplicate.
- Identification. Assign a stable identifier, independent of filename and location.
- Characterisation. Read and preserve technical metadata, compute the checksum, detect the actual format.
- Description. Add context: project, place, people, subject, rights. This is the stage everyone defers, and the one nobody comes back to.
- Replication. Build copies following the 3-2-1 rule, one off-site, with a manifest that lets you check each batch.
- Verification. Periodic re-checking of checksums, with a log of discrepancies. Without this stage, the first five are only a snapshot of the initial state.
What breaks a chain in practice
- Erasing the source before verifying. The most common gesture, and the most irreversible.
- Deferred description. Context evaporates within weeks. What isn’t recorded at ingest won’t be.
- An off-site copy never tested. A backup you’ve never attempted to restore is a hypothesis, not a copy.
- Verification left to human initiative. Anything depending on remembering doesn’t happen. A scheduled campaign does.
The principle that holds it together
At every stage, one rule: fail loudly rather than succeed silently. A checksum that couldn’t be computed is not a valid file. An interrupted copy is not a copy. A batch whose count doesn’t add up is not complete.
A system that reads doubt as success will teach you about the problem years too late.
In practice
- Verify the copy before releasing the card.
- Describe at ingest, even coarsely.
- Produce a manifest for every archived batch.
- Schedule verification campaigns instead of deciding on them.
- Test a real restore at least once a year.
Obscura Flow implements this chain as one piece: verification before source deletion, durable identifiers, checksums at import, resumable uploads to remote storage, and fixity audits that only update their timestamp after a successful check.