Storage array employing scrubbing operations using multiple levels of checksums

A storage system comprising:

• a storage array controller;
• and
• a storage array coupled to the storage array controller by an interconnect, wherein the storage array comprises a plurality of storage devices;
• wherein the storage array controller is configured to write data to a first data range in the storage array, wherein the first data range comprises one or more units of data, wherein the storage array controller is further configured to initiate an extent scrubbing operation for the first data range, wherein the extent scrubbing operation comprises reading the data from the first data range from the one or more storage devices comprised in the storage array, calculating an extent checksum for the data read from the first data range, and comparing the extent checksum to a preexisting extent checksum for the first data range;
• wherein if the extent checksum differs from the preexisting extent checksum, the storage array controller is further configured to initiate one or more unit scrubbing operations, wherein each unit scrubbing operation comprises calculating a new unit checksum for a first unit of data, wherein the first unit of data is comprised within the first data range, and comparing the new unit checksum to an existing unit checksum for the first unit of data.