Generating a data stream with a predictable change rate is disclosed, including: receiving a change rate parameter; and using the change rate parameter to provide a modified data stream that differs from a corresponding unmodified non-deduplicatable data stream by an amount determined based at least in part on the change rate parameter, including by: modifying at least a portion of a plurality of data blocks associated with the non-deduplicatable data stream to obtain a corresponding portion of the modified data stream, wherein a data block of the plurality of data blocks is associated with a block size that is based on a segmenting attribute associated with a storage destination.