If you have less than 4 disks, simply add your disk(s) to the box. You can hot-add it if your ReadyNAS supports drive hot-swapping (i.e. NV, 1000S). If your ReadyNAS does not support hot-swap, simply power off the ReadyNAS, add the disks and power on. The newly added disk(s) must be at least the same size as the smallest existing disk. Note that you can add one or more disks at a time. You will be notified by email and through FrontView that the disks will be initialized (this can take several hours depending on the disk capacity). During the initialization phase, you can use the ReadyNAS normally. Once the initialization is done, you will be notified to reboot the ReadyNAS. Upon reboot, the expansion process will occur (this can take several hours or much longer depending on your drive capacity and the number of files in your data volume). You can monitor the status via RAIDar. Upon completion, you will be notified that the volume has been expanded.