What is a cold backup (offline backup)?
A cold backup is a backup of an offline database. It is also known as an offline backup.
Cold backups are one of the safest ways to back up because they avoid the risk of copying data that might be in the process of being updated. A cold backup requires some downtime because users cannot access the database during the backup.
A cold backup can be done to another disk on the server where the database resides. However, if the server crashes, the backup will also be gone. To prevent this problem, admins often copy the cold backup to tape or disk on a different server.
A USB drive or external hard drive can also undergo a cold backup by unplugging the drive after the backup. However, the USB drive or external hard drive must be reconnected for each subsequent backup.
Benefits of cold backup
Cold backups are immune to power surges and electrical interruptions. They cannot be interrupted by a virus or intruder. In addition, cold data backups prevent accidental overwrites or deletions.
A cold backup ensures a consistent backup, but cannot be used for any systems that require continuous, 24/7 operation. To ensure the files remain unchanged during the backup, users must log out of and cease any activity on the system.
If an organization backs up data to an off-site facility, it can perform cold backups from a copy of the data. Data files do not change during a cold backup process, ensuring the database is in a consistent state when it returns to normal operation. Cold backup servers remain off until a disaster event occurs and users need to go into disaster recovery mode.
Cold backup vs. hot backup vs. warm backup
Cold backup sites are relatively inexpensive to maintain. They are typically an off-site space where data needed to return service to users can be obtained and then delivered to the site before the recovery process can begin. The delay involved when moving from a cold data backup site to full operation can be lengthy. When system downtime must be minimal, a hot backup is a good alternative.
A hot backup can be done even as users access the database. However, if the data is altered during the backup, it can be inconsistent. A hot backup uses compute resources, so it can affect database performance. Hot backup servers generally receive ongoing updates from the production server and are ready to take over as soon as a failover event takes down the production server.
In a warm backup, the server is powered on but not performing any work, or it is turned on from time to time to get updates from the server being backed up. Warm backups are usually used for mirroring or replication.