md5 Use an md5 sum of the data area and store
it in the header of each block.
+ crc64 Use an experimental crc64 sum of the data
+ area and store it in the header of each
+ block.
+
crc32 Use a crc32 sum of the data area and store
it in the header of each block.
crc16 Use a crc16 sum of the data area and store
it in the header of each block.
+ crc7 Use a crc7 sum of the data area and store
+ it in the header of each block.
+
null Only pretend to verify. Useful for testing
internals with ioengine=null, not for much
else.