Is the Write Back enabled on the Areca controller? What happens if you write to the volume that has the 1,4 T 64%? Check in the Console screen and enter CTRL ALT N then select the NIC you using to send files and check the "Info" option to see if you have any TX or RX bad or dropped packets. You could try to do a Repair filesystem from the Extended tools from Console (Keep in mind it will do a reboot). Then try again with the file.
- installed newest firmware on Areca-Controller
- reboot the NAS
Addendum: 4 last years replaced disks are show as current SATA150 (Backplane supports SATA300)
all other disks: are current SATA300
replaced this 4 ST1000NM033 by HUA721010CLA330 => current SATA300
Nice feature: ST1000NM033 in a newer Eurostor-Box with newer ARECA: current SATA600 (disk is able)