Definition - What does Warm Standby mean?
Warm standby is a redundancy method that involves having one system running in the background of the identical primary system. The data is regularly mirrored to the secondary server. Therefore at times, the primary and secondary systems do contain different data or different data versions.
Techopedia explains Warm Standby
A warm server, is turned on periodically to receive updates from the Warm Standby machine. In contrast, a hot standby system is running simultaneously with another identical primary system. On failure of the primary system, the hot standby system immediately takes over to replace the primary. Both systems are assured to have identical data as it is mirrored in real time.
Also in contrast, a cold standby system is a redundancy method which involves having one system as a backup for another identical primary system. The cold standby system is only called on when the primary system fails.