Designer : OpenSCAD
Slicer : Cura
Printer : Creality 3D CR-10
Material : PLA Optimus 1.75 White (filament-abs.fr)

Compact Stackable Raspberry NAS with PSU and between 1 and 4 hotplug HDD

IMPORTANT

If you use spinning disks (not SSD), they will heat a lot (up to 80°C). I added a 120x120 5V cooling fan on the side to keep temperature below 30°C.

20190125-EDIT: I also designed an enclosure to include the 120x120x25 5V fan

This is the second version. The v1 was hard to assemble (typically the bullet connectors for the power rail).
It was way too high and not so compact.

I compacted the HDD and RPi levels
I changed the stack assembly to use M2x3mm screws
I removed the bullet connectors with a tradeoff by soldering.

Goal

A small NAS using a Raspberry, with 4 HDD and a power supply, to save energy and space. It does not have to be lightining fast for my home needs (backups, photos/movies/music repository, ...)
Result : 16 Watt instead of 70 Watt!

Design constraints

I currently use a small standard PC with 2x1TB HDD in RAID as a storage for backups with RSync. This is an overkill. I want to upgrade the usage with OpenMediaVault (http://www.openmediavault.org/) to store

• my backups (RSync and/or Rsnapshot,
• my movies (for XBMC/Kodi),
• my music (for XBMC/Kodi),
• a MacBook Air's timemachine backups.

I want to optimize the energy+space vs usage ration with :

• Dedicated sized Power Suply Unit
• Raspberry Pi 2 (no need for Wifi, Ethernet cable sharing the USB bus is fine)
• 4x 1TB HDD (SSD would be better, but far too expensive for this project and not justified)

I don't want to power the HDD from the RPi USB sockets, I chose to Double USB to SATA cable adaptor to get power directly from the PSU to the HDD
I don't want to power the RPi from its side USB power socket (bad location, power supposed clean, ... I'll power the RPi from the GPIO pins
I wont use any kind of UPS (in case of power failure, no client will connect) and it would be difficult to design such an UPS for the RPi and 4 spinning disks. I'll work at the software layer to make it robust against unexpected poweroff.
I want to be able to plug/unplug HDDs easily, without a tray
I want to be able to mout/unmount the stack to scale up/down using few screws and with backplane power rail connectors
I want to be able to insert/remove the RPi SD card without unmounting anything
The HDD bay needs to be able to receive low profile only 2.5 HDD form factor (L=100mm, W=700mm H=9.5)
I still hate to remove and clean support material from my printings... The design should be supportless ! ;)

Bill Of Material :

• Power cord
• micro power switch 250V/3A : https://www.banggood.com/20pcs-250V-3A-Mini-Boat-Rocker-Switch-2-Pin-Plastic-Button-ONOff-SPST-p-1044250.html
• Generic Power Supply Unit AC 110-220V To DC 5V 6A 30W : https://www.banggood.com/AC-85-265V-to-DC-5V-6A-30W-Switch-Power-Supply-for-Car-LED-Strip-Lights-p-967013.html
• Raspberry Pi 2
• Raspberry Pi 2/3 Copper Heat Sink Heat Sink https://www.banggood.com/Raspberry-Pi-23-Copper-Heat-Sink-Heatsink-With-3M-Special-Thermal-Cooling-Paste-p-1045808.html
• SD card
• 4x 1TB HDD : https://www.ldlc.com/fiche/PB00235600.html
• 4x Double USB to SATA cable adapter : https://www.banggood.com/Double-USB-2_0-Adapter-Cable-715pin-Male-to-Male-for-Laptop-2_5HDD-Hard-Disk-Drive-p-1026866.html
• M3 6mm screws (the screws used in computers to secure all the parts together)
• dupont lines with connectors (M/F) for the power rail

Printing

Before printing

You might need :

• to check and adjust the size and location of the screw holes for the PSU
• to check and adjust the size and location of the screw holes and walls for the SATA-USB PCB adaptors depending on yours
  Even if you buy the same references from the same supplier, the item can change, sometimes. ;)

HDD level (between 1 and 4 times):

• Printed on CR-10, with PLA in 2 hours and 33 minutes (approx. 38g of PLA)
• Nozzle 0.4mm
• first layer 0.375 mm @ 195°C/75°C, other layers: 0.2 mm @ 190°C/70°C
• 3 top layers, 3 bottom layers, 3 perimeters
• Infill : 20% triangle
• Horizontal expansion : -0.2mm
• Skirt suggested, Brim recommended, no support

RPi level

• Printed on CR-10, with PLA in 2 hours and 6 minutes (approx. 41g of PLA)
• Nozzle 0.4mm
• first layer 0.375 mm @ 195°C/75°C, other layers: 0.2 mm @ 190°C/70°C
• 3 top layers, 3 bottom layers, 3 perimeters
• Infill : 20% triangle
• Horizontal expansion : -0.2mm
• Skirt suggested, Brim recommended, no support

Possible improvements:

• Add status LED (Power)
• Add status LED (System starting/started/stopping/stopped blink/loadHeartBeat/blinking/off)
• Add status LED (OMV process stopped/starting/started no process=off, process but no http=blink, process and http=on)
• Add an high voltage fuse
• Add a graceful reboot/shutdown GPIO push button (short/long press)
• Redesign the HDD level with a tray