ST8000VN004

Geizhals.eu lists the drive as CMR - I can't say 100% for sure if that's true. But I have no reason to doubt it. So far I have had no problems with it, but it is also used as RAID0.

We offer the version you are looking for Seagate IronWolf (8 TB, 3.5", CMR) Due to the problem with counterfeits in Europe, there is currently no availability, so this variant cannot be offered.

Yes, I bought the same ones here for the DS923+ and they work perfectly.

Yes, depending on the raid configuration, this is possible or you will destroy everything. With a mirrored RAID you can do this step by step by first swapping a hard drive for an 8TB. As soon as the RAID is intact again, you can swap the smaller disc for an 8TB. This will not work with a striped RAID. If the disks are not set up as a RAID, you can swap them and copy the data if necessary.

I bought 4, but at different times. The first I bought turned out to be a 2M2101, the later 3 drives were all 3CP101's.

The actual RPM of this hard drive is 7200 RPM. This is a known display error on our part. We are working to rectify the problem as quickly as possible.

I have the 1x8 TB version in my desktop, which is muffled, and I have 4x 6TB in my Synology 1019+, which is in a closet. It is known that Ironwolf are "slightly" louder than WD Red, but we are talking about 1-2dB maximum. Of course, the question is what you mean by "unbearably loud". I myself can say that under a long full load, a slight buzzing can be heard, but no roaring/rattling (if I leave out the cabinet or the housing cover). So I would rather say that one of your hard disks has a defect. That's why I would recommend a SMART test via Synology DSM. Hopefully it will show the culprit. I had a DoA once before, because the hard drive was not doing well in the post. So it would not be surprising.

No, this would be a first ;-) Every normal HDD/SDD in 3.5", 2.5" or even m.2 comes without any mounting material. Exception are some Server HDD/SSDs which are already mounted to a caddy: HPE 12G 2.5" SAS 2.4TB 10k (2.40 TB, 2.5") Mounting frames and screws are part of your computer case.

The catch is with the disc size: the compatibility list does not specify a disc over 6 TB, not even a WD!

Can someone delete the question is on the wrong product

I can only answer for DS1513 and DS2413. There the disk works without problems. Synology has a compatibility list on their site. And if any other 8TB is on there, the chances of this one working are very high. Disk size restrictions depend almost exclusively on the chipset used, and that applies to all disks.