SilverStone Technology RM51 5U Rackmount Server Chassis - Dual 180mm Fans & Enhanced Liquid Cooling Support | High-Performance Server Case for Data Centers, IT Racks & Enterprise Storage Solutions (SST-RM51)

Pros:1) Only NAS chassis I'm aware of with 12 hot-swappable drive bays + 120mm to 360mm radiator support. Most other chassis either give you a lot of drive bays with limited CPU cooler support, or have a wide range of CPU cooler support, but limited drive bays.2) Built like a tank. I don't have this in a server rack mount, so its been taking its fair share of beating when I've had to move it around, but its sturdy as hell.Cons:1) Built like a tank. This thing is heavy even without all 12 bays populated...2) Very sharp corners and panel edges. I hope SilverStone takes some time to find ways to round off the sharp corners and panel edges. I can see someone cutting themselves when rotating this around for maintenance since its already so heavy.Other Notes:Someone else mentioned that the 3 OEM 80mm x 15mm hard drive fans are noisy. They are. According to the manuals the default fan profile when the fan headers are plugged into the backplane is drive temps >= 45C means 99%-100% fan speed. 12 fully populate bays will mean your drives will be 45C or more, so I wouldn't recommend using the backplane fan headers unless you like your fans always at basically 100%I did try a bunch of different brands of fans to test out, and the OEM fans are probably the best 80mm x 15mm fans to have in terms of noise to cooling capabilities.I tried 3 Noctua NF-A8s (80mm x 25mm) mounted behind the backplane bracket towards the PSU (compared to the OEM fans being mounted in front of the backplane bracket towards the backplanes), and while those were definitely quieter they could not sufficiently cool down twelve 3.5in drives without being on 100% speed (and at that point you can definitely hear them).If you want to mount 80mm fans from other brands in the same orientation as the OEM fans then you can get away with anything up to 80mm x 20mm. Otherwise you can go up to 80mm x 25mm without issues when mounting the fans behind the backplane fan bracket towards the PSU.You can technically go as deep as 80mm x 38mm when mounting the fans behind the backplane fan bracket instead of the default OEM orientation, but you may run into some issues with thread holes from the mobo preventing flush mounting of your fans.I settled on 3 Sanyo Denki 9GA0812P1H611 80mm x 38mm fans (mounted slightly crooked) at 6% - 14% duty cycle. That is sufficient for keeping all 12 drives between 38C and 45C during heavy drive loads while keeping the noise as low as possible.