It is recognized that disks are an inherently unreliable component of computer systems. Mirroring is a technique to allow a system to automatically maintain multiple copies, or a dual backup (meaning that the data is redundant on all hard drives that exist in the mirror) of data so that in the event of a disk hardware failure a system can continue to process or quickly recover data. Mirroring may be done locally where it is specifically to cater for disk unreliability, or it may be done remotely where it forms part of a more sophisticated disaster recovery scheme, or it may be done both locally and remotely, especially for high availability systems. Normally data is mirrored onto physically identical drives, though the process can be applied to logical drives where the underlying physical format is hidden from the mirroring process.