I picked up 2 HGST He8 8TB drives for my EX2 Ultra. These drives run pretty cool unless transferring massive amounts of data & even then they don’t get to hot in a desktop environment.
I had a 6TB Red drive in it that would top out 43c & the fan was always on from boot-up. Usually ran in the lower 3000 RPM range. Installed the HGST He8’s in my EX2 Ultra. At first the fan on the Ultra wouldn’t turn on. Drives were getting to 50c while transferring files & no fan activity. I rebooted it a couple times & the fan turned on running around 4400 RPM. Then it spun up to 9000 RPM for a while.
Currently the drives are at 41c & 43c and the fan is running at 8333 RPM during a hour long data transfer. The fan has never ran this high.