Learning term
3-2-1 backup rule — Storage and backups
3-2-1 backup rule: The recommendation for three copies on two media types with one offsite copy. This card shows its role in “Storage and backups” and a safe diagnostic path.
Orientation
3-2-1 backup rule: The recommendation for three copies on two media types with one offsite copy. At this level, separate purpose, input, and visible result. Place 3-2-1 backup rule within Storage and backups before changing settings or files.
Practical use
When data is missing or storage fills up, use `lsblk`, `df -h`, and a restore test to establish utilisation, mounts, and recoverability relevant to 3-2-1 backup rule. Start in a sandbox with neutral examples. Record the expected state, make one controlled change, and compare status output, application behavior, and logs.
Technical understanding
3-2-1 backup rule: The recommendation for three copies on two media types with one offsite copy. Technically, 3-2-1 backup rule connects through interfaces, configuration, state, or dependencies. Trace data from input to output and check versions, permissions, networking, storage, and resources separately.
Operations and debugging
When data is missing or storage fills up, use `lsblk`, `df -h`, and a restore test to establish utilisation, mounts, and recoverability relevant to 3-2-1 backup rule. In production-like operations, use measurable signals, least privilege, reproducible configuration, and a documented rollback. Preserve evidence, isolate the cause, and verify the correction with the same test.
Exercise
Try it safely
When data is missing or storage fills up, use `lsblk`, `df -h`, and a restore test to establish utilisation, mounts, and recoverability relevant to 3-2-1 backup rule. Open an isolated test environment and run “df -h && du -sh /srv/example-app”. Write down the expected output first, do not alter production data, and record one safe next diagnostic step.
df -h && du -sh /srv/example-appQuick check
Can you explain the purpose, observable state, and most common failure source of 3-2-1 backup rule — Storage and backups in one sentence each? Which evidence would you preserve before changing anything, and which repeated test would prove that the correction actually worked?