Mixing brand model and size to upgrade storage space?

volpone wrote:
I've checked partition log. Seems all 4 disks are 512 sector. So i'm afraid i will need to full backup and factory reset my NAS prior to expand my array.

Well you could replace two disks one at a time, hot-remove disk, wait say half a minute then hot-add again, disk will be wiped, then you need to wait for resync to complete then repeat for second disk. Then replace the other two disks one at a time with the higher capacity disks. If you go down this route I'd recommend running the "Test Disks" boot option. It is a good idea to check if a disk is failing. The hot-swap route is an option though I'd prefer the backup and factory default route.

volpone wrote:
I have an other "small" NAS and several external USB HDD, but i miss a single backup volume with sufficent space (2TB) . Any pointer to a full data backup procedure (near 2TB needed) on several devices ?

Well you could put one of the new 2TB drives in a USB enclosure and backup your data to that. Then do another backup of your most important data to your other NAS and external USB hard drives.

Then do a factory reset and hot-add (add while NAS is on) the 2TB disk you put in a USB enclosure to the NAS.