I'd like to get some clarity on a matter.
At the moment my NSS4000 is running in Raid5 with 4 * 1TB drives.
I would like to upgrade these to 4 * 2TB drives.
I'm fairly sure that when i swap the drives 1 by 1 and let them rebuild, that everything will be fine.
But what i would like to know now is that when all drives have been upgraded will i be able to extend the capacity of my shares?
You can expand your RAID 5 capacity one drive at at time as you suggest, instructions for doing this can be accessed in the NSS on-line "help" screens as well as the Admin Guide for the NSS4000. Keep in mind however that the total capacity is limited to the smallest drive size in the RAID array so you won't see the full capacity of your 2TB drives in the array until ALL of the 2TB drives have been installed and reconfigured. Also, be advised that should there be a HD failure while expanding/building the RAID 5 array you could have data loss. Because of this it's HIGHLY recommended that you backup your NSS data before performing this type of upgrade.
Once you have replaced your 1TB drives one at a time and allowed each of them to be configured in the array 1 at a time (could be a lengthy process) you can then edit the capacity of your Volumes up to the new total available RAID 5 capacity, which in turn dictates the storage capacity of your shares. To expand your Volume capacity from the MANAGER MENU, click on STORAGE>VOLUMES, then click the "Edit" button on the Volume you which to expand.
Hope this helps and Good Luck!