Checksums and Their Use in ZFS

End-to-end checksums are a key feature of ZFS and an important differentiator for ZFS over other RAID implementations and filesystems. Advantages of end-to-end checksums include:

• detects data corruption upon reading from media

• blocks that are detected as corrupt are automatically repaired if possible, by using the RAID protection in suitably configured pools, or redundant copies (see the zfs copies property)

• periodic scrubs can check data to detect and repair latent media degradation (bit rot) and corruption from other sources

• checksums on ZFS replication streams, zfs send and zfs receive, ensure the data received is not corrupted by intervening storage or transport mechanisms

Checksum Algorithms

The checksum algorithms in ZFS can be changed for datasets (filesystems or volumes). The checksum algorithm used for each block is stored in the block pointer (metadata). The block checksum is calculated when the block is written, so changing the algorithm only affects writes occurring after the change.