Fractal Design’s Node 304 MiniITX case is a popular, sleek NAS enclosure (e.g. for use with FreeNAS). It has room for 6x 3.5" full height HDDs.
My partner in technical crimes has created a mounting frame for adding up to four 2.5" SSD (max. 7 mm thickness) without occupying the 3.5" bays. With his consent (and a minor improvement I made), I'm sharing this one with you.
The speed switch for the front fans on the rear of the enclosure has to go, as we are attaching the fixture for the frame to those screw nuts. Simply strip the switch and attach the fans straight to the motherboard, you want them to spin at full speed anyway (they are super-quiet).
Make sure to check out my other Node 304 mods.
Thanks for your tip! :)