Data redundancy mechanism in storage

In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system performance. Storage device may also have the problem such as bit malfunction or data loss, which require data redundancy mechanism to protect data. The following solutions are commonly used and valid for most storage devices:


  • Device mirroring (replication) – A common solution to the problem is constantly maintaining an identical copy of device content on another device (typically of a same type). The downside is that this doubles the storage, and both devices (copies) need to be updated simultaneously with some overhead and possibly some delays. The upside is possible concurrent read of a same data group by two independent processes, which increases performance. When one of the replicated devices is detected to be defective, the other copy is still operational, and is being utilized to generate a new copy on another device (usually available operational in a pool of stand-by devices for this purpose).
  • Redundant array of independent disks (RAID) – This method generalizes the device mirroring above by allowing one device in a group of N devices to fail and be replaced with the content restored (Device mirroring is RAID with N=2). RAID groups of N=5 or N=6 are common. N>2 saves storage, when comparing with N=2, at the cost of more processing during both regular operation (with often reduced performance) and defective device replacement.


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