Modular Open‑Frame Micro‑ATX Case for 20+ HDDs

Modular Open‑Frame Micro‑ATX Case for 20+ HDDs (3D Printed)

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This is a 3D‑printed, modular open‑frame case designed to support a micro‑ATX motherboard and 20 or more 3.5" hard drives.
It’s ideal for DIY NAS builds with large storage arrays, or for anyone who needs a compact high‑capacity HDD solution.

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✅ Positive Notes

• Modular open‑frame structure for easy assembly and fast printing time
• Supports micro‑ATX motherboards
• Holds 20+ standard 3.5" HDDs (40 HDD slots in the photos)
• Rear fan mount for good airflow
• Most parts can be joined together using small printed interlocking blocks (LockingTab)

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❌ Negative Notes

• I didn’t design any cable management at all, so… good luck
• Some screws and threaded inserts are required to assemble the PieceHolder, the HDDLocks, and the fans
• All the power and fan cables shown in the photos are handmade by me — make sure you have the necessary skills before creating DIY cables, as mistakes can be very expensive

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🖨️ Printing Notes

• Print in ASA or ABS (ASA shown in the photos)
• Do NOT print it in PLA — it will definitely deform or melt over time (see photos of the old blue PLA case)

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🤯 Crazy Tip

If you’re using a large number of HDDs (especially SAS drives), your PSU will almost certainly struggle to provide enough current on the 5V rail.
I solved this by adding a 30A DC‑DC buck converter, which draws power from the 12V rail and converts it to 5V.

Additionally, if you build your own HDD power cables, make sure they are properly sized.
An 18 AWG cable I used had too much voltage drop on the 5 V line to power 10 HDDs in series.
I added extra 2 A DC‑DC converters at the end of the line to reduce the voltage drop.

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📦 My HDD SAS Setup

• LSI SAS 9300‑16I PCI Express Board
• RES2SV240 RAID Storage Expander

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💡 Bonus Tip

I developed a program to automatically spin down SAS HDDs.
If you're interested, you can find it here:
https://github.com/Daxel90/SAS_SpinDown