Since you linked to my thread, I will take a crack at these.
1. can the 900P be used as cache ? i understand it actually works - see here, but is it officially supported ?
I still don't see any official support mentioned but at this point the system with a 900P as Optane cache has been up and running flawlessly for more than a month.
Scheduled optimize tasks are working correctly and the system is in credibly fast. 2 cumulative updates for windows have been installed without issue.
That being said, I had a backup plan if this did not work. I would have simply installed the OS on the P900 as a SSD and used my SATA SSD as a data drive.
It is a risk if you attempt to replicate my setup but since I got it working twice (one in testing and again in the final system) I am confident that you wont have an issue.
2. if the above is possible (or at least working), can i split the drive, i.e. use half as cache and half as a drive ?
The setup process for Optane wipes out the drive. I do not believe that anything that was there before this task is retained including partitions.
3. are there any plans to allow caching of more then a single physical drive ?
I have seen rumors of data drive Optane caching but nothing definitive.
4. assuming 3 will be supported, will i actually see a gain when caching a fast NVMe SSD, (i have a Samsung 960 Pro 2TB drive)
Data drive caching will still likely be restricted to SATA drives. The problem with a theoretical scenario where you cache a 960 Pro with Optane is that the sequential speed of the 960 Pro is actually better than Optane.
What I hope to see instead would an all in one M.2 SSD where 1 side is a 1TB NAND SSD and the other is Optane cache. Correctly implemented you would have a SSD with both blazing 4KQ1T1 speed and blazing sequential speed.
5. will the U.2 version work with any M.2 PCIe slot ? specifically i am using the Gigabyte Z370 Aorus 5 gaming board, with 1 x M.2. slot used for the boot SSD.
M.2 that supports NVMe, U.2 and PCIE gen 3 X 4 lanes are all the same base port.
Any motherboard with M.2 that supports NVMe on that port is compatible with a M.2 -> U.2 converter. The U.2 Optane drive comes with a cable and adapter that allows for M.2 install. Just make sure that you order the one that mentions this, I think there is a variant that does not come with the cable but you can just buy on anyway.
Z370 in general should always support both Optane and M.2 NVMe gen 3X4.
In the case of your specific motherboard you have this:
- 2 x M.2 connectors (Socket 3, M key, type 2242/2260/2280/22110 SATA and PCIe x4/x2 SSD support) (M2M_32G, M2A_32G)
- 1 x M.2 connector (Socket 3, M key, type 2242/2260/2280 PCIe x4/x2 SSD support) (M2P_32G)
Intel® Optane™ Memory Ready
You are good to go.