Exemplary method, system, and computer program product embodiments for data verification in a storage system are provided. A read of data is asynchronously submitted to nonvolatile storage media. A read of a first checksum signature is submitted to a solid state, sidefile memory location of a storage controller in the storage subsystem. The first checksum signature is representative of the data previously written to the nonvolatile storage media. A second checksum signature is calculated from the read of the data. The first and second checksum signatures are compared. If a match is not determined, a critical event is reported.