XFS is what Zyxel defaults the file system on the volume to; I wasn't aware you could define a seperate filesystem and have it work properly.
You can swap around disks between various ZyXEL NASses, and keep your data. So the NAS has to be down-compatible. So far ZyXEL has used reiserfs, xfs, ext3 and ext4 for their data partitions, when I remember well. I *think* any filesystem will be accepted, as long as the kernel supports it.
I do want to maintain a RAID1 array if possible to help keep my data secure
In that case you should *not* use RAID1. Raid is about availability, not about security.
Raid protects you against failure of a single disk. But that is all. It doesn't protect you against:
- Accidentally deletion of files (#1 in data loss).
- All disks are in the same unit, which mean one hazard threatens them all:
- A failing power supply which last voltage peak toasts all connected harddisks (or at least enough to break your array).
- Dropping the whole disk unit, killing all disks.
Further, because most raid arrays start with n equal disks, and all disks are subject to the same wear, the odds that a 2nd disk will die while rebuilding an array after a failing first one, breaking the array, is bigger than you like, and is getting bigger.
It gets bigger because disks are getting bigger, while their MTBF and throughput doesn't grow as fast. This means that syncing an array takes more time, which is more time for a 2nd disk to fail.
For security you need backups.
It was also quite stable with XFS/RAID1 with my previous 250GB drives. Could it be less stable for bigger disk capacities?
Well, yes. Bigger disks mean bigger filesystem structures, bigger sector numbers, ... In your case the sector numbers have exceeded a 32 bits number, which can open a whole new area of bugs.