How Hiberden Verifies Every Copy
Updated July 14, 2026
Most backup tools tell you a copy was written. Hiberden goes one step further: it proves each copy is identical to the original, byte for byte, by reading the copy back and checking it, not by trusting that the write succeeded.
A fingerprint for every archive
When Hiberden seals an archive, it computes a fingerprint of the whole thing: a checksum, a short code derived from the data. Its useful property is that the code changes if any part of the data changes, even a single bit. Two copies with the same fingerprint hold the same data; two that differ, even by one byte, produce different fingerprints.
Hiberden records that fingerprint in its catalog when the archive is created. It is the reference every copy is later measured against.
Reading back, not trusting the write
A successful write is not proof. Disks develop bad sectors, tapes can shed bits over the years (a slow decay often called bit rot), and an upload can be cut short without raising an error. So after Hiberden writes each copy, it reads that copy back off the actual medium and recomputes the fingerprint:
- Disk, NAS, and cloud copies are read straight from the storage.
- Tape copies are read back through LTFS, the tape's own filesystem.
If the fingerprint of what it read matches the one on record, the copy is proven intact and marked Verified. If it does not match, the copy is marked Failed. If the copy has gone missing, it is marked Missing. Verified is never assumed from a successful write; it is earned, every time, by a real read-back.
What the states mean
- Verified: read back and confirmed identical to the original.
- Failed: read back, but the fingerprint did not match, so the data on that medium has changed. Re-write that copy from a good one.
- Missing: the copy was not where the catalog expected it.
Because each copy is checked on its own, an archive shows Covered 3 of 3 only when all three copies have passed independently. That is the difference between hoping you have three good copies and knowing you do.
Why it matters
Silent corruption is the quiet failure mode of long-term storage: a file decays on the shelf and nobody notices until the day it is needed, years later. Verification turns that silent failure into a loud one you can act on now, while a good copy still exists to re-write from. It is also why restoring is safe: Hiberden re-checks the fingerprint on the way out, so every restore is itself a verification.
For the curious: the fingerprint is a cryptographic checksum computed over the whole archive, the same idea used to verify software downloads and secure connections. It is strong enough that two different sets of data will not realistically share one.
Related: Verified 3-2-1 Archiving covers how many copies to keep, and Restore your data shows verification on the way back out.