Dualparity

Dualparity is a data protection concept that uses two independent parity blocks to safeguard striped data against multiple failures or corruption. It is most commonly implemented in storage systems that support two-parity configurations, such as RAID-6 and RAID-Z2. In these schemes, data is distributed across several disks, and two parity streams are computed from each stripe. With two parity blocks, the system can recover original data if up to two disks fail or their contents become unreadable.

In practice, dualparity relies on a linear error-correcting code, often derived from Reed-Solomon algorithms, to generate the two parity blocks. During normal operation, reads access only data blocks; when a disk fails or a block is corrupted, the remaining data blocks plus the two parity blocks are used to reconstruct the missing information. RAID-6 commonly employs two independent parity calculations to provide this protection, while RAID-Z2 implements a similar capability within the ZFS framework.

Trade-offs include increased storage overhead and write complexity, since updates must be applied to both parity blocks. Rebuilds after failures are more robust than single-parity schemes but can take longer and place higher stress on remaining disks. Dualparity does not protect against all forms of data loss, such as multiple simultaneous failures beyond two, unrecoverable read errors during rebuild, or data corruption that bypasses parity.

Dualparity is popular in enterprise storage, NAS devices, and some cloud storage architectures where higher resilience against dual failures is prioritized over maximal capacity efficiency. It is not a replacement for regular backups or data integrity verification.