M4 Mac Mini - External Thunderbolt Drives Limitation

[bzgnyc2]

@bzgnyc2 : You summarized the issue and behavior really well! I did report this to Apple. The 1st support engineer indicated this might be a power draw limitation on the board itself but hesitated to document anything formally. The other support techs wouldn’t even acknowledge the issue, just kept reading the specs and asked me to exchange the product. Btw, I have support cases open from 2020 (USB speed) that i never got any updates for.

As for Thunderbolt certified devices and the 15W power draw limit, I had 3 OWC Envoy Express enclosures. Apparently, these were the 1st Thunderbolt 3 certified bus powered devices. Do all 3 connect at the same time? Nope. The Acasis Air enclosure exhibits the same behavior as it is Thunderbolt only (no USB fallback).

Unfortunately, I now see this issue has come up before with previous models of the Studio:

Why can't I use all 4 Thunderbolt ports o… - Apple Community

discussions.apple.com

Studio Ultra - Simultaneous use of Bus Powered TB devices limited? (title edited)

Today I discovered that I cannot connect more then three thunderbolt drives (and the BenQ display using USBC) to my Studio Ultra. On the back four ports, I have connected: 1. BenQ SW321C 2. ProGrade TB3 CF Express card reader 3. & 4. Orico TB4 enclosure w/Samsung 980 Pro NVMe SSD If I connect...

forums.macrumors.com

 

[G5isAlive]

Unfortunately, I now see this issue has come up before with previous models of the Studio:

Why can't I use all 4 Thunderbolt ports o… - Apple Community

discussions.apple.com

Studio Ultra - Simultaneous use of Bus Powered TB devices limited? (title edited)

Today I discovered that I cannot connect more then three thunderbolt drives (and the BenQ display using USBC) to my Studio Ultra. On the back four ports, I have connected: 1. BenQ SW321C 2. ProGrade TB3 CF Express card reader 3. & 4. Orico TB4 enclosure w/Samsung 980 Pro NVMe SSD If I connect...

forums.macrumors.com

For whatever its worth, I routinely connect 4 externally powered SSD's to my Studio Ultra 1

 

[bzgnyc2]

For whatever its worth, I routinely connect 4 externally powered SSD's to my Studio Ultra 1

Yes it appears to be a matter of simultaneous power to TB devices rather than bandwidth (and I would have thought harder to route 4x64 Gbps of a system's PCIe bus around the system and out the box than 4x15W). It appears through the 2025 Mac Studio that only 2 bus-powered TB devices can be connected at once. Self/externally-powered SSD and bus-powered SSD connected through a TB hub the workaround for now.

Unfortunately, externally powered TB5 SSD appear somewhat rare right now (and I don't see too many externally powered TB4 SSD outside of docks either). Inserting TB hubs into the configuration appears to work though a bit messier (both technically and physically).

 

[PaulD-UK]

@bzgnyc2 "I don't see too many externally powered TB4 SSD outside of docks either".
That's because the only TB4 device chip Intel developed, Goshen Ridge, is only for dock or 3-port TB4 hub use, and can only allocate 10Gbps of PCIe 3 data to SSDs.

USB4 performs that function, allowing all the available data bandwidth (~32Gbps) to SSDs, or you use TB3 Titan Ridge enclosures to get PCIe 3x4 lanes (less video bandwidth) to SSDs.

"I would have thought harder to route 4x64 Gbps of a system's PCIe bus around the system and out the box..."

Because its low voltage low power TTL data its easily routed the short distance from the SoC to the Retiming chip to the port. Trace lengths are designed to be minimal length.

Power at 15w x4/6 is much harder to accommodate (judging by the real life performance of the Studios).
I suppose when you think about it, only one port at a time can handle incoming USC PD charging power on MacBooks, but higher voltages there allows higher wattages than bus power to SSDs.

 

[adonis3k]

I "had" 3 x 4TB NVME enclosures connected to my Mac mini M4 Pro, but everytime you connect the 3rd one it would run slow, stutter and disconnect. Looks like I will be running 2 and a 3rd SSD which are all working fine.
Apple is taking the pi55 imo