X-RAID vs. 2xRAID-1

Jarkod wrote:

...I was thinking 2xraid-1 could be a bit safier because when one drive fails, I'll have another one with data (other scenarios aside). At the end of a day I'll have data on vol. 1, 1:1 copy on vol. 2 and a backup on a usb drive. Or am I completely mistaken? What does xraid do to the second drive, how does this protection work? How is data stored on it; can I retrieve it from the second driveit e.g. by connecting it in a PC and mounting in Linux?...

I thought I answered most of this.

(a) xraid with 2 disks is mirrored. Every write to the volume is literally written to both drives in parallel. Since the disks are written together, the data on them would be precisely the same up to the point of failure. If a drive fails, all your data remains accessible through the NAS. You can in principle mount either disk in another linux system, though it would need to support the btrfs file system.

So this maximizes data availability, and enables volume expansion even while you access your data, and allows data access to continue as usual if a disk is being replaced. In all these cases, the users don't know the expansion, etc. is happening - it is invisible to them.

(b) Your scheme by contrast is not invisible to the users, and does not support volume expansion. It is more economical on space, and for the shares you are copying you get a little more protection from user mistake - since you can access the older copy if you want to. You have some insulation against any glitches that corrupt the file system itself, since you have a unsynced copy. But if there is a failure, you would lose any work that was done after the last backup. Like (a) you can in principle mount either drive in a linux system that understands btrfs.

That's the trade-off. Both will work. I wouldn't say your method is safer than xraid - it has some advantages, and some disadvantages.