Actually, the 5 drives are striped RAID-0, using a Windows NTFS dynamic disk. The 20TB are fully usable.
The MP34 4TB are TLC. https://www.amazon.com/dp/B08Z7LN8NM . No longer available. My purchase history shows $240 each in April 2023. It dropped to $200 later on that year. It looks like there are some on Ebay for $350 now.
I just ran Crystaldiskmark 9.0.2, with 64GB file size, and it showed 3506 MB/s read / 4359 MB/s write, sequential. Not sure if I exceeded the buffer. It's a bit odd that the write speed is faster, but I can't complain. My OS boots from a 256GB 15 year old SATA SSD drive, in a hotswap bay.
I have been giving some thought to switching the OS to Proxmox and ZFS. Win11 Pro is not ideal for running the services I have, including a Home assistant VM currently in VMWare Pro, Plex server, and Unifi.
As far as getting 8 NVMe drives in my system, no, I couldn't do it with the current mobo/controller I have. You can't physically fit two X16 cards in the Prime X570 Pro, as it only has one x16 slot. It supports either x16/x4 slots, or x8/x8/x4 slots. I'm using x16 for the Hyper-X card, and x4 for the X550-T2 NIC. The box idles at 50W. The NVMe drives use only about 1W idle each. If I removed the NIC, and found some working dual-NVMe x8 cards, I could get 5 drives through PCIe with x8/x8/x4, plus 2 on the motherboard, which would make it 7. I actually tried 2 of these cards that claim to do 2 drives with x8 : https://www.amazon.com/dp/B09PGDMWKH . I couldn't get the bifurcation to work. Each card only saw one drive.
I had actually originally purchased 6 MP34 drives, assuming I could connect 2 on the motherboard, and 4 on the HyperX card. I could only get 3 out of the 4 drives to work on the Hyperx card. Never figured out why, and returned one drive to Amazon. Looking at my history,
Bifurcation support is an issue. This is why I bought an Asus X570 motherboard and Asus branded Hyperx card. It's a 16 lanes card, and it's weird that I could get only 3 drives (12 lanes) working on the card.
Anyway, if you only need 5 NVMe drives, then the setup I have works. For 8 or more, you would probably need a Threadripper motherboard to have enough PCIe lanes. Much more $$$, not to mention the power consumption.