Sorry for the late reply,
I probably don't fit the standard computer user with 20 SSD's over three RAID controllers, and still counting :-)
In my I would place the LR catalogue, either on the TEMP/SCRATCH drive or add a forth SSD drive for it.
SCRATCH disk size, all depends on the type of work you do, I do large pano's so I need a large temp/scratch disk approx. 1TB
but I would just add two 120 SSD;s and stripe them, in my case I use 8 SSD's for this for the improved speed increase!
All my spinning disks are in NAS
Where would you put the LR catalogue in the set up above?
In my new build I am considering 2 SSD drives and 2 regular spin drives for data.
For the SSD with my OS and apps i will go with reliability and an Intel. But I am not sure about the SSD that I will dedicate as a SCRATCH AND TEMP DISK. What is the minimum size SSD for this task? (I like to be frugal). And I understand the that SSDs seem to break down more often than spin drives. Are ADATA, Samsung or Crucial drives reliable as a cost cutting choice?