STORAGE RESILIENCE

Why RAID is not a backup

RAID can help a server keep working after certain disk failures. A backup gives you another recoverable copy of the data. Those are different jobs.

What redundancy can help with

Mirrors and parity can let a storage set survive one or more drive failures, depending on the layout. That can reduce downtime and make replacing a failed disk less disruptive.

What it does not protect against

If you delete a folder, corrupt files, encrypt the array with ransomware or physically lose the server, the redundant disks can contain the same problem. A controller or filesystem failure can also affect the entire storage set.

Snapshots are useful but still not enough alone

Snapshots can make accidental deletion and unwanted changes easier to reverse, but snapshots stored only on the same hardware do not protect against loss of that hardware.

Keep an independent copy

Important photos, documents and configuration deserve a copy that is separate from the live server. For irreplaceable data, an off-site copy protects against events that affect the whole home or device.

Test recovery

A backup process is only useful if you can restore from it. Test individual files and, for important self-hosted services, practise restoring enough application data to rebuild the service.

Use the NAS capacity calculator to see what redundancy does to usable storage.