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Question about QNAP TS-h973AX and u.2/SATA caching

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Nov 11, 2010
So I decided to replace my old QNAP NAS with a QNAP TS-h973AX. The new one has the same storage layout as the old one...5HDDs and 4SSDs for caching

On the old NAS I used five 8TB HGST HDDs in RAID 5, and I used 4 Samsung 512GB SSDs as cache (NAS has 32GB RAM) This worked fine.

On the new NAS I had planned to use the same layout...five 18TB HGST HDDs in RAID 5 and four 512GB SSDs as cache

BUT, after I received the new unit I noticed two of the 2.5" SSD bays MUST use U.2 SSDs, not M.2 SSDs

I have two PCIe Gen 4 nvme SSDs 1TB in size spare on the shelf currently so I bought two "M.2 to U.2 adapters", planning to install the nvme SSDs in the adapters and then use the adapters in the two u.2 bays.

This is where I start to "lose the bubble" because I do not know what impact this change will have on performance due to 2 of the SSDs being U.2 and the other 2 being normal SATA SSDs...the Sizes of the NVME drives are 1Tb while the SATAs SSDs are 512GB and use a slower interface (I would imagine)

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?
It will be as fast as your slowest part.

1/2/3. That seems to be a preference thing, no? About the only worry is with performance, which again should be as fast as your slowest part.

I hope that helps.
Just putting this our there.... With drives that big in a RAID5, the odds for a successful rebuild if one dies is ....slim due to URE's when the array is rebuilding. Not to mention it will take for-freaking-ever. You got backups? I would die if I lost more than 40TB of data, you got all the disks in the array, and no hot spares.

As far as your actual question, I would try option 2 and see if the adapters play nice and don't cause issues. That will be most performance. I would NOT mix the the protocols, ie nvme and sata on the cache tier.