More generally, a hot standby can be used to refer to any device or system that is held in readiness to overcome an otherwise significant start-up delay.
Examples of hot spares are components such as A/V switches, computers, network printers, and hard disks.
It may be considered that the probability of a second failure is low, and therefore the system is designed simply to allow operation to continue until a suitable maintenance period.
The hot spare disk reduces the mean time to recovery (MTTR) for the RAID redundancy group, thus reducing the probability of a second disk failure and the resultant data loss that would occur in any singly redundant RAID (e.g., RAID-1, RAID-5, RAID-10).
The concept of hot spares is not limited to hardware, but also software systems can be held in a state of readiness, for example a database server may have a software copy on hot standby, possibly even on the same machine to cope with the various factors that make a database unreliable, such as the impact of disc failure, poorly written queries or database software errors.
When the master unit fails, an automatic failover to the hot spare occurs within a very short time and the outputs from the hot spare, now the master unit, are delivered to the controlled devices and displays.
The controlled devices and displays may experience a short blip or disturbance during the failover time.