Too late I found that the ShareSpace does not support these drives. After nights of struggling with this, I found a forum post below that confirms that is the case. Now, only the WD20EADS-type is supported. However, these are not for sale at the larger retailers here, only the WD20EARS-disks are.
This was in an attempt of upgrading the 4 TB ShareSpace to 8 TB.
Is there any hope that a future firmware update will support the WD20EARS-drives?