With ZFS, all data and metadata is verified using a user-selectable checksum algorithm. Traditional file systems that do provide checksum verification have performed it on a per-block basis, out of necessity due to the volume management layer and traditional file system design. The traditional design means that certain failures, such as writing a complete block to an incorrect location, can result in data that is incorrect but has no checksum errors. ZFS checksums are stored in a way such that these failures are detected and can be recovered from gracefully. All checksum verification and data recovery are performed at the file system layer, and are transparent to applications.
In addition, ZFS provides for self-healing data. ZFS supports storage pools with varying levels of data redundancy. When a bad data block is detected, ZFS fetches the correct data from another redundant copy and repairs the bad data, replacing it with the correct data.