Glossary · Cloud & Hosting

Backup

A backup is a separate copy of data kept so it can be restored after deletion, corruption, hardware failure or attack.

Updated October 6, 2026

A backup is a copy of data stored separately from the original so that it can be restored after accidental deletion, corruption, hardware failure, malware or other loss.

Why it matters

Backups are the last line of defense. Replication and RAID protect against hardware failure but faithfully copy mistakes; a backup lets you go back in time.

A common guideline is the 3-2-1 rule: three copies, on two different media, with one stored off-site. A backup counts only if you can restore from it, so regular restore tests matter.

Example

0 2 * * * pg_dump mydb | gzip > /backups/mydb-$(date +\%F).sql.gz

This cron entry dumps a PostgreSQL database at 02:00 each day. A good setup also copies the file off the server and alerts if the job fails to run.

Common mistakes

  • Keeping backups on the same server or account as the live data.
  • Never testing a restore, then finding the files are empty or incomplete.
  • Not monitoring the backup job, so it silently stops for weeks.

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