No more criticism (previous opinion)
The rebuild went perfectly well. You have to be patient, a RAID system takes a long time to set up. From 2TB 5600 rpm to 12TB 7200 rpm = about three days of incessant work for the machine. Once it's done, it's a piece of cake... In relation to my last comment, the disks were making noise because they were extremely stressed during the RAID reorganisation. Now, at cruising speed, everything is fine. Access times are much better thanks to the 7200 rpm and the cache system. We now have a little more than 10TB out of the 12TB (5% is used by the NAS system in addition to the disk structure). Finally, there is less expensive, there is also more expensive. At the top of the range. The brand of the NAS manufacturer. Very good hardware.