TerraMaster Official Forum

TLDR:
TOSHIBA HDWQ140 (N300 4TB) drives are not recognized at startup in bays 4 and 5, but recognized on startup in other bays (1,2,3,6). Seems like harware bug.
Full story:
Recently i brought new T6-423 NAS. The initial setup was simple:
1x m.2 nvme samsung 1TB as single disk
3x sata toshiba n300 4TB as RAID1 storage pool at bays 4,5,6
I copied some data on them and the setup worked perfectly. Some reboots was applied and worked perfectrly.
After that i added:
12TB toshiba n300 as single disk at bay 1.
another sata toshiba n300 4TB as single disk at bay 2.
I copied some data on them and the setup worked perfectly. Some reboots was applied and worked perfectrly.
After that i added:
250GB samsung SATA SSD at bay 3 without storage pool creation. and shutdown the system.
Issues begins there. After boot the drives at bays 4 and 5 was not recognized by kernel and RAID 1 was degraded. In logs at /var/log/messages i found that kernel thinks that bays 4 and 5 are empty on boot. Other drives was successfully recognized. I have done some investigations and found that drives from bays 4 and 5 are in good condition and working perfectly in other PC. So I removed SSD drive from bay 3 and plug faulty drive to bay 3 and reboot the NAS. Drive was recognized perfetly on boot and RAID1 rebuild was initiated automaticaly.
After that i have tryed diffirent compositions and found that all of my TOSHIBA HDWQ140 N300 4TB (i have 4 drives of this capacity) are not recognized on boot at bays 4 and 5, but sucessfully recognized at other bays. I note that my TOSHIBA N300 12TB is sucessfully recognized at any bay.

This seems to be affected by your SATA SSD.What was it used for before?
If you encounter this situation again, please generate and download the log report in TOS > Technical Support > Report Issues, and then send it to our support team mailbox or customer service window of the official website homepage as a network disk sharing link for analysis.

That normal SSD was used in other PC sometime. And after that, was used by SATA-USB adapter (Orico) to transfer data from QNAP to TMNAS.
I found that there are only BAY 1 and 2 SATA ports are visible to BIOS. So I conclude that your NAS use separate SATA controller(s) for ports 3-6. I think this controller is not good enougth. I have looked at logs and found that the kernel think thouse bays are empty. I don't see any point in sending logs. This is definitely a hardware problem.