Raid changing automatically

mdgm wrote:
...With X-RAID2 single-redundancy with two or more disks, the volume capacity would be that of all the disks added together less the capacity of the largest disk.

Which is 12 TB if you go with 4x4TB drives (4*4TB - 4TB -> 12 TB). The NAS will report this in TiB (1024*1024*1024*1024 bytes = 1 TiB), so it should report ~10.9 TiB.

That is, 12*(1000*1000*1000*1000)/(1024*1024*1024*1024) = 10.91. The calculation ignores space for the OS partition and other overhead, so you will see a bit less.

The capacities with 4 TB drives and single redundancy xraid2 are:
1 drive - no redundancy: 4 TB (or 3.6 TiB)
2 drives - redundancy: 4 TB (or 3.6 TiB)
3 drives - redundancy: 8 TB (or 7.2 TiB)
4 drives - redundancy: 12 TB (or 10.9 TiB).