Controls the checksum used for data blocks. On the ZFSSA, all data is checksummed on disk, and
in such a way to avoid traditional pitfalls (phantom reads and write in particular). This allows the
system to detect invalid data returned from the devices. The default checksum (fletcher4) is
sufficient for normal operation, but paranoid users can increase the checksum strength at the
expense of additional CPU load. Metadata is always checksummed using the same algorithm, so this
only affects user data (files or LUN blocks).