Pearity

My Mac mini server runs Plex, but it has no room for 3.5-inch drives, so the media library had to live somewhere else. The only off-the-shelf box I could find that connects straight to a Mac was OWC's ThunderBay 8, at about $850, and it wouldn't fit a 10-inch rack anyway. I was already planning a mini-rack, and some napkin math showed that eight drives would fit between its uprights.

There was already a printable 8-drive holder for mini-racks, but every time you swapped a drive you had to plug cables into the back of it. I wanted the clean, OEM feel of a real rack server: slide a drive in and it's connected.

Drives slide into custom caddies and plug into an 8-bay SATA backplane, sold as a spare part for the Jonsbo N3 NAS case. Drives are swapped with the power off, since it isn't built for hot-swapping. A Flex ATX power supply behind a switched power inlet runs the backplane and fans. The backplane's eight SATA connectors fan out to two mini-SAS cables, which reach the server in one of two ways:

• Thunderbolt 3: an M.2 8-port SATA controller inside a Thunderbolt 3 NVMe enclosure turns one Thunderbolt port into eight SATA ports. This is how my Mac mini connects.
• Direct: a PC can run the mini-SAS cables straight to its own M.2 SATA card or HBA.

The anti-vibration TPU fan screws are im.jackharvest's design.

• Design around an off-the-shelf backplane. Instead of cabling each drive, I built the enclosure around a cheap, easy-to-find SATA backplane, so drives slide in and connect like they do in a commercial rack server. Before committing to it, I asked half a dozen AliExpress sellers for schematics to make sure they were all selling the same board.
• Apple-inspired looks. The front takes its visual cues from Apple's Xserve RAID, and the Mac mini shelves in my rack carry the same idea forward.
• Tool-free caddies. Small nubs on each caddy snap into the screw holes on the sides of the drive, so you don't need screws.
• Front-to-back airflow. The first design had five 40 mm fans. The final one has two 92 mm fans on TPU mounts at the back, pulling air in through the front, across the drives, and out the back. The body is printed in ASA-CF so it holds up to heat without sagging.
• A standard power supply, inside. My first plan was a 12 V LED supply plus a buck converter for the 5 V rail. A Flex ATX PSU gives both rails and standard drive connectors in one part. Keeping it inside keeps the OEM look: plug in one power cable and one Thunderbolt 3 cable and you're done.
• Enough bandwidth, not too much. Hard drives can't use Thunderbolt's 40 Gbps, so the SATA controller runs on a PCIe 3.0 ×2 link, about 1.7 GB/s. That's still more than the drives or my network can use.
• Easy to print and mount. It's three main parts plus eight caddies, with print orientation already set in the MakerWorld .3mf file. Three screws hold each front ear. Racks vary in depth, so there are three rear panels: ears at the very back for custom racks, ears 260 mm from the front for GeeekPi and Tecmojo 12U racks, or no rear ears at all.

• The backplane was 0.9 mm too long. It was longer than the enclosure's maximum internal width. I sanded mine down to fit, but sanding a circuit board means fiberglass dust and PPE, and I didn't want that in anyone's build instructions. So I cut a small slit in each side wall, and now the backplane slots in without changes. The trade-off is a small gap on each side, which you can't see once it's in a rack.
• The drive slots were 0.5 mm off. Early drafts spaced the slots 27 mm apart, but the backplane's connectors sit 27.5 mm apart. That was close enough to fit, but repeated drive swaps would have strained the connectors. I re-spaced the slots to match the board.
• The parts list crept up in price. I first planned to use a Thunderbolt dock with Ethernet, USB-C, USB and Thunderbolt ports on the back. Once I added it all up, the build cost was close to OWC's ThunderBay Flex 8, which defeated the point of building my own. I dropped the dock to keep it cheap.
• I printed about a dozen betas. This was my first 3D design project. It took close to a dozen full test prints before every part printed cleanly and fit, and four months to get from the first CAD model to release. Lesson learned: to test a fix, print only the part you changed, not the whole enclosure.

Mine is the storage behind my Mac mini media server, holding seven drives: two in a RAID 1 mirror and five for backups and bulk storage. It has run since August 2025 with no issues, and the numbers back that up:

• Speed: 158 MB/s write and 189 MB/s read on one drive of the RAID 1 pair (Blackmagic Disk Speed Test), about what a single hard drive can do.
• Workload: I added two new drives 10 months ago, and they've run nonstop since. One shows 7,481 power-on hours over just 20 power cycles, with 30.1 TB written and 34.9 TB read.
• Heat: that drive peaked at 50 °C against a 65 °C rating, averages 31 °C, and has spent 0 minutes over temperature.

The parts cost about $280, roughly a third of the ThunderBay 8's $850. If your server already has mini-SAS ports, you can skip the Thunderbolt enclosure and SATA controller and spend about $190.

• Thunderbolt 3 NVMe enclosure (ACASIS TB34): $65
• ASA-CF filament for the body and back panel: $48
• Flex ATX power supply, 400 W: $44
• Jonsbo N3 8-bay backplane: $29
• M.2 8-port SATA controller: $22 (on sale; $61 list price)
• Two mini-SAS-to-SATA breakout cables: $18
• Two 92 mm fans: $17
• Power inlet with switch and fuse: $12
• Spade connectors, fan guards and power cord: $20
• PLA for the caddies and faceplate: $5

Prices checked October 26, 2026, before tax and shipping. Drives not included.

On MakerWorld, other makers have downloaded it 400+ times, saved it 800+ times and posted 60+ completed builds. Two builders have remixed it, one to fit smaller A1 mini printers, and another printed one for an Unraid server planned around eight 16 TB drives. One reviewer reports it's "been working perfectly for the past 3 months."

• A real power switch. The switch I wired in only cuts the PSU's incoming power. It doesn't use the PSU's own on/off line. Before the rack was on a UPS, the PSU sometimes didn't restart properly after a brief outage, so I wired it to stay on all the time. A redesign would add an external switch on the PSU's on/off line.
• Drive status LEDs. The backplane has a header for a status LED for each drive. A new front panel could bring those to the front, for more blinky lights.
• A universal Thunderbolt cradle. The cradle was sized for the Fantom Drives eXtreme enclosure, which has since been discontinued. The ACASIS TB34 fits the same pocket with no changes, but a cradle that fits a range of enclosures would make the design last longer.

• Pearity on MakerWorld: files, parts list and build guide
• The r/minilab thread