X-RAID vs. 2xRAID-1

Thanks for explanation but still have a couple of questions.

StephenB wrote:
The configuration you linked to is sometimes called "jbod". You have two completely separate volumes of 2 TB each. You can use them anyway you want, and there is no failure protection. You can if you wish use backup jobs to regularly copy data from one to the other.

Failure of what? Disks or data? If I create a backup job and will have the same data on both disks, isn't it enough to protect against disk failure or data loss?

StephenB wrote:
If you are using your NAS only for backups, then either jbod or xraid will do. If you are using your NAS for primary storage, then xraid is better for most users. Either way you need a backup on a different device if you truly want to protect your data from loss. Don't imagine that RAID ensures that your data safe - it does not.

The point is I'd like to use it for both: a Lightroom folder with photos accesible from different computers and a backup of users' home catalogues. My thinking was to move a Lightroom folder with photos to vol 1 and make a backup home of calogues also on vol 1. Then make a copy of vol 1 on vol 2 and this way I'd kill two birds with one stone. But you're saying it's not enough. What happens to a drive/data when the other drive fails (in 2xRAID-1 configuration)? I thought it stays ok, data is safe and I can insert a new drive and manually sync it with the old one.