A cold backup, also called an offline backup, is a database backup during which the database is offline and not accessible to update. This is the safest way to back up because it avoids the risk of copying data that may be in the process of being updated. However, a cold backup involves 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, the cold data backup is often copied 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.
Cold backups cannot be interrupted by a virus or intruder, and are immune to power surges and electrical interruptions. In addition, cold data backups prevent accidental overwrites or deletions.
Cold backup vs. hot backup vs. warm backup
A cold backup ensures a consistent backup, but cannot but used for any systems that require continuous, 24/7 operation. No users should be logged in and no activity should take place to ensure that files are not changed in any way during the backup. If you back up data to an off-site facility, cold backups can be performed 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 are turned off until a disaster event occurs and users need to go into disaster recovery mode.
Cold backup sites are not expensive to maintain and are little more than an appropriately configured space in a building where everything needed to return service to your users must 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 minimized, a hot backup can provide an alternative to a cold backup. A hot backup can be done even as users access the database, but if the data is altered during the backup, it can be inconsistent. A hot backup can also impact database performance because it uses compute resources. 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.