Hi there,
If you just have to replace one disk, then I think the process should be pretty straightforward - I found another very helpful thread here on the WD Community walking through the process of upsizing the disks:
One thing I was considering was just upsizing one of the disks for now, and upsizing the second disk later - something which WD support (seems incorrectly) told me wasn’t possible - but I think this is indeed possible by following through the steps in that other thread I just linked to.
However, in my case things became a little more complicated as I had 2 disks both (suspiciously) fail within weeks of each other. Well, not quite fail, but the NAS was showing red lights and warning me that the disks needed to be changed. While I already had separate backups anyway, the disks were still good enough to read all data off them onto a temporary portable HDD, and then I just put 2 brand new WD Red 6TB disks into my enclosure and started from scratch, so to speak.
I’m going to investigate the SMART data on the “bad” disks, and if suitable, I might resell them - with full disclosure of course.
