QNAP TS-h973AX caching

[notarat]

So I decided to replace my old QNAP NAS to a QNAP TS-h973AX and I noticed some differences between the old and new. The new one has the same physical layout of 3.5" and 2.5" in a 5+4 configuration...

On the old NAS I used five 8TB HGSTs in RAID 5, and I used 4 Samsung 512GB SSDs as cache (NAS has 32GB RAM)

On the new NAS I'm using five 18TB HGSTs in RAID 5 and had planned to use four 512GB SSDs as cache (NAS has 32GB RAM)

BUT, 2 of the 2.5" bays must use U.2 drives not M.2 (so 2 of the drives I bought are superfluous (I can return them...no biggie)

This is where I start to "lose the bubble". There's nothing in the QNAP manual or on their site that says I can't use M.2 to U.2 adapters to use a couple PCIe Gen 4 nvme SSDs 1TB in size in those two drive bays as cache while I use normal SSDs in the other 2 bays...but I'm wondering how/how much it will affect performance.

I guess if I were to pare it down to the bare essential question(s) it/they would be:

1 - Should I just use a couple SSDs and leave the U.2 bays unused?

2 - Should I do the opposite and use the two U.2 bays (with the afore-mentioned adapters and NVME M.2 SSDs) and leave the 2 SATA bays unused?

3 - OR should I just fill all the U.2's with 1TB nvme' using the adapters AND use the sata ones with normal SSDs?

 

[bigddybn]

Not positive but pretty sure they intend those two U2 bays to be used as cache. Might want to double check the software isn't going to whine if you try to use them for dumb storage instead.