Immutable backup
An immutable backup is a backup protected so that, for a defined retention period, it cannot be modified, overwritten or deleted — including by an authorized administrator or a process running with their privileges. This protection is enforced at the storage layer itself, independent of application-level permissions, which makes it the final, tamper-proof line of defense in a backup strategy.
How an immutable backup works
The technical foundation is the WORM (Write Once, Read Many) model — data, once written, can be read any number of times, but for the duration of the lock it cannot be changed. This is implemented in several ways: through Object Lock in S3-compatible object storage, dedicated backup repositories with a set retention, or read-only snapshots of a file system. The lock usually comes in two modes: governance, which allows exceptions for selected privileges, and the stricter compliance mode, where no one can tamper with the backup until the retention period ends.
Practical application
Immutable backups have become a standard defense against ransomware, because modern attacks deliberately destroy backups before encrypting production data. They extend the classic 3-2-1 rule, now expanded to 3-2-1-1-0: three copies of data, on two different media, one off-site, one immutable or offline, and zero errors when verifying restores. Immutable backups are also frequently a regulatory requirement in finance and healthcare. When implementing them, it pays to align the retention period with your RTO and RPO targets and with a broader disaster recovery plan, so that locked copies genuinely shorten the time to recover after an incident.
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Najczęstsze pytania
Why does an immutable backup protect against ransomware?
Modern ransomware deliberately encrypts or deletes backups before hitting production data, so the victim cannot recover. An immutable backup is locked at the storage layer for a set period, so even a compromised administrator account cannot tamper with it.
What is the WORM model?
WORM (Write Once, Read Many) is a storage principle where data, once written, can be read many times but cannot be overwritten or deleted for a defined retention period. It is the technical basis of immutable backups, originally derived from archival media.