PowerScale OneFS 9.2.1.0 CLI Administration Guide

Data mirroring

You can protect on-disk data with mirroring, which copies data to multiple locations. OneFS supports two to eight mirrors. You can use mirroring instead of erasure codes, or you can combine erasure codes with mirroring.

Mirroring, however, consumes more space than erasure codes. Mirroring data three times, for example, duplicates the data three times, which requires more space than erasure codes. As a result, mirroring suits transactions that require high performance.

You can also mix erasure codes with mirroring. During a write operation, OneFS divides data into redundant protection groups. For files protected by erasure codes, a protection group consists of data blocks and their erasure codes. For mirrored files, a protection group contains all the mirrors of a set of blocks. OneFS can switch the type of protection group as it writes a file to disk. By changing the protection group dynamically, OneFS can continue writing data despite a node failure that prevents the cluster from applying erasure codes. After the node is restored, OneFS automatically converts the mirrored protection groups to erasure codes.