A plurality of data sets is maintained, wherein each data set comprises an index block and a plurality of data blocks. An index block size is determined for redefining the plurality of data sets, based on an amount of space left unused in index blocks of the plurality of data sets, wherein for determining the index block size greater weight is provided to those index blocks with lesser unused space in comparison to those index blocks with greater unused space. A data block size is determined based on whether the plurality of data blocks is used more frequently for direct processing or used more frequently for sequential processing.