I recently bought a WD My Cloud Mirror NAS which includes 2 2TB hard drives running in RAID 1 by default. That effectively gives me 2TB of storage space which is plenty for now. I know I will eventually run out, though, and when I do, I'd like to be able to increase the capacity while keeping everything contained within one unit. One of the features of the device is being able to increase the capacity by plugging in external USB drives but I would rather not do that. If anything, I would rather reserve that feature for performing backups for offsite storage.
I'm a little annoyed (especially by WD) that I can't find any information on this topic, even on their community forums. The only information I can find is on replacing failed drives. It seems like a no-brainer for me. Why would anyone replace an entire NAS just to upgrade the storage capacity when the drives are replaceable? My guess is that they can be upgraded and here's how I think it can be done: Replace one drive, let the RAID rebuild, replace the other, then expand the volume. I'm not sure about a few things though. Does the device support larger drives than the original ones, can you upgrade them one at a time, and if it's even possible, how do you expand the volume? Is it automatic or do you have to do it manually?
I'm just not sure about all this. I have an idea but I'm not willing to buy new drives unless I know it will work.
Best Answer
With RAID 1, both drives MUST be the same size. So if you're upgrading the drives, then you can't just rip one out, put one in and expect it to rebuild. However, if the drive is the same size it should work fine. But seeing as you're wanting to expand the volume, it's not going to work. You're going to need to backup your data onto an external device, take out your hard drives (both of them), put your new drives in, create the new RAID array then put your stuff back on.
The TL;DR version: You can't mix hard drive sizes with RAID 1, which means you cannot expand the RAID volume.