A method is used in validating data in a storage system. The method writes host data to the storage system during processing of a host I/O operation, where the host is in communication with the storage system. The storage system writes host data and test data associated with the host data to a storage device of the storage system. The method reads the host data and the test data from the storage device for validating the host data, and evaluates the test data to determine whether the host data has been written correctly by the storage system to the storage device. Upon determining that the host data has not been written correctly by the storage system to the storage device due to a failure, the method evaluates the test data to determine a cause of the failure.