This is a remix of two existing 3.5" HDD holder models, designed to provide multiple configurations.

Please note that at this time, this is Untested. 
I anticipate this to print just fine, however until I test it - this disclaimer must remain.

This is the first model I've had the pleasure to edit. Constructive criticisms and any tips/remixes are welcomed. 

Included STL files:

HDD_3.5_v1_Unmodified.stl – Original 6-bay rack.

https://www.printables.com/model/190070-35-hdd-storage-holder-6x

Non-stackable.

Holds standard 3.5" drives only.

HDD_3.5_v1.1_6x_Stackable.stl – Stackable 6-bay rack.

Holds 6 3.5" drives.

Bottom has short divider stubs for stacking while not doubling the filament usage.

Use as a modular unit to stack racks securely. 

HDD_3.5_v1.1_12x_SideBySide.stl – 12-drive side-by-side configuration.

Not stackable; intended as base unit.

Saves filament by sharing the middle wall.

HDD_3.5_v1.1_12x_SideBySide_Stackable.stl – 12-drive side-by-side with stackable bottom.

Bottom divider stubs allow stacking.

Combines side-by-side layout with stackable functionality.

All files hold standard 3.5" HDDs (26mm thick).
 

Designed for efficient printing and minimal filament usage, while keeping drives stable and secure