since my secondary backup NAS (Zyxel NSA310 w/Debian) has left the building some days ago, I was thinking about an easy and cheap solution holding a single drive. I came to that:
Cost 23,90€ on Ebay.
I used a 3,5" 3TB HDD drive instead the mentioned 2,5", pulled of my defective Zyxel. Drive is lying on the PCI-Slot (no need for any screw), power and data cables reside over the RAM-Banks. The lid will close (keeping the drive in position), really fine.
This cable is shorter than described; don´t go for it with a 2,5". You have to find a longer one for that case.
mSATA SSD Drive 32GB: https://www.amazon.de/gp/product/B01N9ZWJV2 as system drive. Cost: 14€, now slightly more
Not the fastest, not the best, but cheap enough to give it a try.
Parts are all in place and lid closed, so I´ll take it to work and install debian, than OMV.
I will report and when its ready, I´ll make a photo.