I didn't know I could pull on drive from a pair and replace it with a second empty drive that was larger. I did do that many years ago when one drive in a pair went bad, but I replaced it with an identical drive.
You can easily do this with any of the NAS systems that have been around for a while, and in theory you should be able to do it with an internal RAID set up, running software RAID or hardware RAID off a PCI card.
BUT don't do it unless you have a solid and current back up of the data, it is not uncommon for the remaining drive to fail while the array is being rebuilt.
It is also possible the controller you have running the RAID may not like discs that are very different from each other, or it may not allow you to expand the volume with out formatting the array and starting from scratch.
I never thought it much but just this week I saw someone post that a hacker infected their NAS with ransomware and the hacker wanted a ridiculously large sum of money to unlock it.
I would like to have an external drive enclosure accessible to multiple devices with my home network. But I don't want to expose it to hacking.
A NAS on your network is no more or less vulnerable than any other other device.
If you share folders off the NAS on the internet, and there is vulnerability, then there is a chance someone could find it and exploit it.
If you have a mapped drive on your PC and you download malware then that could access and damage the data on the mapped drive.
If your hosting a website, a gaming server or similar that is open to the internet, then there is a chance someone could find it and exploit it.
But if your responsible and only using it for file sharing with in your own network and use the remote access tools built into the NAS protected with a strong password then it is quite safe.
And since you will have the NAS backed up separately, if anything does happen you just format the NAS and restore everything from the back up.
