RAID and backups solve different problems. A redundant array may keep storage available after certain drive failures. A backup provides a separate recovery point when valid data has been deleted, corrupted or lost with the machine. You may need both.
Map the failure to the recovery method
| Event | Planning requirement |
|---|---|
| One member disk fails | A suitable redundant layout, monitoring and replacement process |
| An operator deletes a database | A recoverable earlier copy |
| The application writes bad data | Versioned backups and a way to identify a valid restore point |
| The whole server becomes unavailable | Copies accessible outside that machine |
| A backup credential is compromised | Access separation and protected retention |
A mirror normally reflects changes to its members, including unwanted writes. RAID 0 provides striping without redundancy. Other layouts have different capacity and failure characteristics; do not choose a level from the disk count alone.
Document the actual layout
- Record physical drives, serials, controller or software RAID configuration and usable capacity.
- Configure alerts for degraded state and failed backups.
- Keep application-consistent backups outside the array.
- Write down how a failed member is identified and replaced.
- Test a restore to an isolated destination and record recovery time.
A rebuild consumes resources and is not the same as a verified backup. If an array is degraded, preserve recoverable data and follow the correct platform procedure. Do not create a new array over existing members while trying to repair it.
Check the application after recovery
A mounted filesystem is only the first check. Validate database integrity using supported tools, inspect recent records and test the application. Review what writes may be missing from the recovery point and reconcile them deliberately.
Monitor drive-health signals and use the backup planning guide for off-machine copies and restore objectives. The same recovery principles apply to physical and virtual servers.
Sources and references
Hosting documentation. Publication and update dates reflect this edition.
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