What Does RAID 51 Mean?

RAID 51 is a type of nested RAID level that provides RAID 1-based mirroring on each RAID 5 array.


It is similar to RAID 1, where each element is a disk with native redundancy capabilities. It requires a minimum of six disks to operate.

RAID 51 is also known as RAID 5+1.

Techopedia Explains RAID 51

RAID 51 is implemented by mirroring or implementing RAID 1 on an entire RAID 5 array in addition to the parity information. It is generally created using software and hardware-based RAID techniques where RAID 1-based mirroring is implemented through an operating system on the hardware-based RAID 5 array.

RAID 51 is specifically designed for enhanced backup availability and high fault tolerance capabilities. RAID 51 is considered a parity set of mirrored disks, hence RAID 5 is followed by RAID 1. It can remain operational or protect from data loss even after losing four of the six minimum configured disks.


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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.