Why am I unable to expand the capacity of a RAID 10 group on a TS-x31 or TS-269H series NAS?
The following NAS series: TS-x31, TS-x31C, TS-x31U, TS-269H, do not support expanding RAID 10 groups by replacing disks one by one or by adding new disks. This is a limitation of Linux kernel 3.2 which is installed on these NAS.
Instead of expanding a RAID 10 group, you can use any empty drive bays or an expansion unit to add new disks, and then create a new storage pool or single static volume.