How do we know our backup data hasn't quietly bit-rotted or gone corrupt?

Files sitting on disk or tape for years can silently bit-rot. A 'completed' job says nothing about whether data is readable in 6 months. Hash verification and checksum-aware filesystems are your safety net.

Try this first

1. 1Pick storage with built-in checksums: ZFS, Btrfs or enterprise NAS with data-integrity scrubbing. Ext4 and NTFS don't detect bit-rot.
2. 2Cloud providers: S3, B2, R2 auto-hash and re-replicate on detection. A key reason to run cloud-immutable alongside local.
3. 3Backup tools: Veeam Health Check, Acronis Backup Validation and NAKIVO Recovery Verification do periodic checksum validation. Turn it on even if it costs IO.
4. 4Schedule scrubs on NAS or filesystem: weekly or monthly depending on volume. On detected error, act before older backups are also unreadable.
5. 5Archive-tier backups (Glacier, Deep Archive, Coldline): ask the provider about integrity guarantees. AWS markets 11-9s durability, but that's after they received it, not against your upload error.
6. 6Document per repo which integrity mechanism is active. At audit you know immediately, and you spot coverage gaps.

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