Someone suggested that my Controllers probably did not support TRIM, and that I should move the cache-drives to be directly connected to my motherboard.
I did that today, and ran TRIM with success
HUGE HUGE difference in transfers now.
Before a simple File Transfer using FTP would stall after a few seconds, sometimes to the extent that FTP did a timeout and the transfer had to be resumed, giving me annoying prompts about overwriting and sh**
Just did a 200 GB transfer with minimal stalls (all less than 4 seconds)
(probably Network Buffer -> SSD cache transfers)
My point: if you are using SSD as cache, you need to use TRIM, it really makes a big difference.
I am very happy.
Connect the cache drives directly to the motherboard if possible
(I did not do any preparation or anything, just unplugged the drives and connected them directly to MB and unraid found them without me doing any configuration)
BTW: I am now running v6.4.1 (no trim issues from command prompt)
My system:
X99 MB in Norco 4224 cabinet, Intel i7, 64GB DDR4
4x 500GB Samsung SSD
14x 8TB Western Digital Gold / Seagate Ironwolf