A:Answer Hi Robinstates, Please be informed that with My Cloud EX4100 you can create a custom NAS with compatible hard drives. Moreover, in order to configure RAID on the NAS the capacities of HDD should be same, otherwise you may use different size HDD. To know more about the drive refer the below link: https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/wd/product/nas/my_cloud/my_cloud_ex4100/data-sheet-my-cloud-expert-series-ex4100.pdf -Need Help? Please see our "'Contact Us" page for information.