A method for data transformation is provided. The method includes interleaving input/output (I/O) processing of files or blocks and rekeying of the files or blocks. The method includes blocking from the rekeying the portion of the file or blocks while the portion of the file or blocks is subjected to the I/O processing and blocking from the I/O processing the portion of the file or blocks while the portion of the file or blocks is subjected to the rekeying. The method further includes writing metadata regarding status of the rekeying of the portion of the file or blocks, and regarding a key applied in the rekeying of the portion of the file or blocks, wherein at least one method operation is performed by a processor. A computer readable media and a system are provided also.