Our CPK tool from my experience is quite accurate and conservative when sizing, using compression ect. I would suggest you have a look at that. You can enable 'Dedupe and Compression' and then under the 'Dynamic Provisioning' tab set just compression and leave off deduplication, hit 'Estimate' and see the numbers updated based on your workload and your hardware configuration.
You can use the HDRE tool to estimate the savings on your workloads too to get an indication of the savings. A Snipit from the userguide below:
Hitachi Data Reduction Estimation Tool can estimate data reduction eɝcienc\ achieved through all of the following data reduction capabilities provided by Hitachi Virtual Storage Platform (VSP) G and F series:
■ Deduplication and compression: Achieve storage eɝcienc\ savings by deduplication and compression through storage controller.
■ Accelerated compression: With Hitachi Accelerated Flash DC2 (HAF DC2), Hitachi Accelerated Flash DC2 (HAF DC2), VSP G and F series oer even greater beneȴts through scalable hardware-accelerated compression. You can answer business demands for high performance and deliver the lowest eective cost. You can estimate the data reduction rate by following the GUI wizard. The window displays the calculation results in a graph. You can use the graph to compare and check the results.