So at the moment I've had similar issues with all NAS Servers I've tried to run from UGreen, TrueNAS and now Unraid.  I've gone over the docs and just can't figure out why it's so darn hard to get these things configured....

 

My current hardware:

 

UGREEN NASync DXP2800

2x Crucial - P3 2TB Internal SSD PCIe Gen 3 x4 NVMe (OS/Cache)

2x IronWolf Pro 20TB-ST20000NT001 (40 TB storage)

 

I'm trying to setup the 2 NVMe's for parity so that if one of them goes boom the OS still works.  As for the Ironwolfs the 40 TB of storage is needed instead of parity.

 

As I've said I've gone through the docs and can't seem to get to a point where I can start the drive arrays.  I'll post some screen shots below of how things are currently configured...do keep in mind that I started off with stuff that made sense to me, but once was done and said and nothing worked I paired back quite a bit:

 

 

 

I get the feeling that there is some sub menu or settig that is currently disabled.  Can anyone give me a bit of guidance?

The OS is NOT installed on any of your drives.   Each time you boot it it is loaded from the OS archives on the USB stick into RAM; your settings are applied from those stored on the USB stick; and then the OS runs from RAM.  

 

If using Unraid 6 then the normal configuration would be to use the 20TB drives in the main Unraid array (either as 2 data drives or 1 data+1 parity and the NVME devices in one or more pools. 

 

With Unraid 7 the main array is optional so you could also use the 20TB drives in a pool (e.g. as a raidz1 redundant pool) instead of the main Unraid type array.

In addition to what has already been mentioned, if you do want to use the parity array.

 

SSDs are not recommended in the parity array,  and in any case, each parity drive must be at least as large as the largest single array data drive.