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Per this "File Transfer Time Calculator", unloading 960 GB at the 20Gbps Thunderbolt 2 speed would require 6m 24s and just 3m 12s over Thunderbolt 3.
So, just like the 22 Gbps cap on PCIe speeds that Thunderbolt 3 has, I found that Thunderbolt 2 similarly has an 11 Gbps cap on PCIe transfer speed. I found this illustrated in this Intel slide:

https://www.aja.com/assets/support/files/3087/en/Thunderbolt2_BandwidthAllocation_2.pdf

What that means is that an external NVMe SSD drive connected to Thunderbolt 2 would only be about 10% faster than being connected to a USB 3.1 Gen 2 port (10 Gbps).

I was not able to find any comparable Intel information on Thunderbolt 1, but I assume it must have a similar data transfer cap. 5.5 Gbps?
 


Ric Ford

MacInTouch
Just did a quick test*, using dd to copy a single 3.6GB file from internal SSD to a Samsung T5 on USB 3.0 (2015 MacBook Pro, macOS 10.12):
116 MB/sec.​
If you're using dd with the default block size, then you probably also enjoy watching paint dry. If you add bs=2M to the dd command, you'll get much more realistic transfer performance. Or, even better, ditch dd entirely, and just use something like cp.
Who knew? Here's the same test using cp instead of dd:

450 MB/sec.​
Copying the file between two volumes on a 2015 MacBook Pro's internal SSD:

593 MB/sec.​
Copying the file from a 2017 iMac 5K’s internal SSD to a Samsung X5 Thunderbolt 3 SSD:

1166 MB/sec.​
 





Ric Ford

MacInTouch
Just did a quick test*, using dd to copy a single 3.6GB file from internal SSD to a Samsung T5 on USB 3.0 (2015 MacBook Pro, macOS 10.12):
116 MB/sec.​
If you're using dd with the default block size, then you probably also enjoy watching paint dry. If you add bs=2M to the dd command, you'll get much more realistic transfer performance.
Sorry, apparently, it wants a lower-case letter, so use bs=2m
Who knew? Here's the same test using cp instead of dd:
450 MB/sec.​
And the same test using dd bs=2m ...

444 MB/sec.​
Copying the file between two volumes on a 2015 MacBook Pro's internal SSD:
593 MB/sec.​
Switching to dd bs=2m gives:

1165 MB/sec.​
 


If you're using dd with the default block size, then you probably also enjoy watching paint dry. If you add bs=2M to the dd command, you'll get much more realistic transfer performance. Or, even better, ditch dd entirely, and just use something like cp.
Very good—thanks for the very worthwhile tip!
 


Here's a benchmark test of one of the first PCIe 4.0 NVMe SSDs. I found it interesting, because it is the only published benchmark of direct NVMe to NVMe copy I've found. It's peformed on the new ASUS X570 motherboard that supports PCIe 4.0 for AMD's recently recleased Ryzen processors. The motherboard is backward-compatible with earlier PCIe versions, which allowed the benchmarks to be performed copying to and from a Corsair PCIe 4.0 drve and a Samsing PCIe 3.0 SSD.
The Guru of 3D said:
Corsair MP600 PCIe 4.0 NVMe SSD review - Final Words & Conclusion
Copying many many gigabytes of movies and ISOs for example, well this SSD laughs at it, and while copying I actually laughed a bit nervously. I mean our 110 GB test file I had to copy towards this SSD from a Gigabit NAS, that took 18 minutes. Then copying the same file from an 870 EVO Plus towards the MP600 ... far less than a minute, bat-poop crazy.
So the results are a bit all over the place really, but it's also priced fairly competitive. I mean this super fast performing M.2. unit costs ~25 cents per GB in retail right now. The unit reveals speeds at 2GB/ to 4.5 GB/s reads sometimes, in writes things are varying more. IOPS performance is great as well, but it does need massive queues and preferably threads for it to be able to show.
Hardware Secrets said:
Everything You Need to Know About the PCI Express
... PCI Express is a point-to-point connection, i.e., it connects only two devices.... On a motherboard with PCI Express slots, each PCI Express slot is connected to the motherboard chipset using a dedicated lane, not sharing this lane (data path) with other PCI Express slots.
 


The new Raspberry Pi 4 announced last month looks like it will be a better desktop machine to learn Linux on, once they patch the USB-C power issues (they used non-standard firmware,so many USB-C cables don't supply power).
They tried to be "clever" (saving the cost of an additional resistor) and didn't follow the USB-C power spec exactly, but what they left out does make a difference - in certain circumstances. It only affects you if you use an e-marked cable (which apparently is only found on expensive USB-C chargers, like Apple laptop chargers) - the cable will not supply power to the Raspberry Pi, because the lack of the resistor in the Pi means that the cable thinks the Pi is an audio device. The Pi works fine with normal (most, I believe) cables. Obviously, the lack of a resistor will not be fixed by a firmware upgrade. They say they will fix it in a future revision of the board.

Full details here:
 


Ric Ford

MacInTouch
Here are a few of the benchmark results I've posted previously (you can probably search for "Blackmagic" to find many of them):
#benchmarks
I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:

Write: 895 MB/s​
Read: 468 MB/s​

That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).

#benchmarks
 


Ric Ford

MacInTouch
I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:
Write: 895 MB/s​
Read: 468 MB/s​
That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).
I flipped them around and tested the 2018 MacBook Pro in Target Disk Mode, connected via Thunderbolt 3 to the 2017 iMac 5K:

Write: 466 MB/s​
Read: 273 MB/s​

Wow, pretty pathetic performance...
#benchmarks
 


I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro.
I’d be interested to see your results if you connected them together by Thunderbolt networking and mount one as a network share (SMB and/or AFP) on the other. I believe you should be able to select a network volume for testing in Blackmagic Disk Speed Test.
 


Ric Ford

MacInTouch
I’d be interested to see your results if you connected them together by Thunderbolt networking and mount one as a network share (SMB and/or AFP) on the other.
I spent quite a while trying but was unable to get file-sharing to work, for unknown reasons. I had tried it previously between Thunderbolt 2 and Thunderbolt 3 systems, and it was much slower than a USB 3.0 SSD, which seemed like a better option for sync'ing files between systems.
 


They tried to be "clever" (saving the cost of an additional resistor) and didn't follow the USB-C power spec exactly, but what they left out does make a difference - in certain circumstances. It only affects you if you use an e-marked cable (which apparently is only found on expensive USB-C chargers, like Apple laptop chargers) - the cable will not supply power to the Raspberry Pi, because the lack of the resistor in the Pi means that the cable thinks the Pi is an audio device.
I may have read the article wrong, but it appears that what's going on is that with this (mistaken) resistor configuration, the Pi thinks the power brick is the audio device. As such, it is trying to supply current out the port (as it would have to if it was powering a pair of headphones, for example) instead of sinking current from the port.

If you don't sink any current, you don't power on.
 


it appears that what's going on is that with this (mistaken) resistor configuration, the Pi thinks the power brick is the audio device.
I've read that, too. When Google's Pixelbook was brand new, I bought one. Grrrr. Google's "state of the art" had only two USB-C ports, where my older Chromebook had a charge port (unfortunately, proprietary), two USB Type-A, MicroHDMI, and a MicroSD slot, in which I kept a 128GB card equal to to the $1,100 Pixelbook's internal eMMC storage. At least both devices had headphone jacks.

I purchased a USB-C dongle/dock that passed through the Pixelbook charging, provided USB Type-A, HDMI, and Ethernet. Did not work well.

I returned the Pixelbook within my Best Buy 14-day window. There may be a place for ChromeOS, and given the Pixelbook's self-constrained connectivity and the nature of ChromeOS, my Rockchip $200 Asus Chromebook Flip was a lot better match. After my experience with the Pixelbook, I've empathy for purchasers of similarly constrained and much more expensive Mac laptops.

That's a long detour from the Pi but does loop back. If the Pi's USB-C were properly designed, it should be possible to extend Pi connectivity with a dongle/dock like I tried with limited success on the Pixelbook. Perhaps that's in the Pi's future, perhaps it's just irrelevant to the Pi use case, but it's not going to happen if Pi's designers don't stick to published standards.
 


Ric Ford

MacInTouch
...I purchased a USB-C dongle/dock that passed through the Pixelbook charging, provided USB Type-A, HDMI, and Ethernet. Did not work well....
My sense from reading customer reviews (e.g. at Amazon or Apple Store) is that many of these USB-C mini-dock type devices are cheap, low-quality products with a relatively high risk of defects — probably more an issue of parts and manufacturing quality than a matter of meeting standards (though I suppose the two can blend). I've also had an unexpected amount of problems with simple USB 3 hubs from several different companies.
 


If the Pi's USB-C were properly designed, it should be possible to extend Pi connectivity with a dongle/dock like I tried with limited success on the Pixelbook.
If they were shipping a proper data+power USB-C port, you would be absolutely right, but that doesn't seem to be their goal. The USB-C port on the Pi 4 is just a power port. There is no data transfer at all on that port. All USB data is via four type-A ports (two USB 2.0 and two USB 3.0).
 


I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:
Write: 895 MB/s​
Read: 468 MB/s​
That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).
I think Apple would say this is "expected". Target Disk mode doesn't directly tie together the Thundebolt (or FireWire) bus and the drive controller with hardware or high-performance firmware, as a good external enclosure would. It's just a convenience for occasional use, implemented in the simplest possible way.

I share Todd's curiosity about what numbers one might see from a Thunderbolt 3-connected "point to point" networked drive, served by a machine with a very fast SSD. It would have to be SMB, I think, but if the protocol implementations are highly tuned, it wouldn't completely surprise me if it were faster than target disk mode.
 


Ric Ford

MacInTouch
I share Todd's curiosity about what numbers one might see from a Thunderbolt 3-connected "point to point" networked drive...
I spent more unsuccessful time yesterday trying to get this to work, and I have no idea what's wrong. Things I tried:
  • disabling firewalls
  • turning off WiFi (so the Thunderbolt connection was top on the Network list)
  • various SMB and AFP combinations/options
  • swapping Thunderbolt ports (though I didn't try every possible combination, and both computers showed "Active" Thunderbolt network connections)
  • different access methods (hostnames, IP addresses, protocols)
  • logging into different user (admin) accounts
It has been pretty frustrating.
 


many of these USB-C mini-dock type devices are cheap, low-quality products with a relatively high risk of defects
I've had those problems, too. Trying to avoid them, the "dongle/dock" I bought was from Anker, a brand which I've found reliable, and at $70, I don't consider it "cheap."

Hard to blame the gadget, though Amazon currently lists it as "upgraded." No way to know if what was "wrong" was the gadget itself, or ChromeOS, or Google's intentional implementation.

The USB-C port on the Pi 4 is just a power port.
Maybe we should consider the "defect" to be a "feature", as I'd suspect the 100 watts that USB Power Delivery could push could be dangerous?

It's the presence of that "universal" Type-C port that frustrates, because it suggests more options.
 


Maybe we should consider the "defect" to be a "feature", as I'd suspect the 100 watts that USB Power Delivery could push could be dangerous?
The official Pi 4 (and recommended) power supply is 15.3W (3A at 5.1V). I assume this was selected in order to satisfy the power requirements of the Pi 4 running at full capacity.

If you were to attach a 100W supply (assuming the board was fixed to properly recognize it), I highly doubt it would try to draw more than 15.3W. I've never heard of a power supply trying to "push" more power than the device is trying to draw. I don't even know if that makes sense, electrically.
 


If you were to attach a 100W supply (assuming the board was fixed to properly recognize it), I highly doubt it would try to draw more than 15.3W
Ever wonder why it is safe to connect an 85-Watt MacBook Pro power brick to an Air that needs only 45? Or how a 45-Watt MacBook Air charger might (eventually) top up a quiescent MacBook Pro?
Ken Sheriff's Blog said:
Macbook charger teardown: The surprising complexity inside Apple's power adapter
There's a lot more circuitry crammed into the compact power adapter than you'd expect, including a microprocessor. This charger teardown looks at the numerous components in the charger and explains how they work together to power your laptop.
Ken Sheriff's Blog said:
Lacking safety features, cheap MacBook chargers create big sparks
Why does a fake charger produce sparks, while a genuine one doesn't? The fake charger constantly outputs 20 volts, so if any metal shorts the connector, it produces a big spark with all its 85 watts of power. On the other hand, the genuine charger doesn't power up until it has been securely connected to the laptop for a full second.
If you were to attach a 100W supply (assuming the board was fixed to properly recognize it),
It's the assumption that the Pi is properly configured that gives pause. That, and the 100-Watt "Power Delivery" USB-C adapter might itself not be configured safely?
 


... I've never heard of a power supply trying to "push" more power than the device is trying to draw. I don't even know if that makes sense, electrically.
No, it does not make sense, electrically.

Technical note: Power supplies we are speaking of are designed as "constant voltage sources" and are not affected by load until the load rises to the capacity of the power supply. Power draw by any device connected to a specification-compliant power supply is entirely under the control of the load device, up to the maximum available power.

Try this analogy: The AC outlet in a typical US home is a nominal 110 Volts AC - a "constant voltage source.”
  • Connect a 100 watt bulb and 100 watts is delivered (~0.91 Amperes).
  • Connect a 10 watt bulb and 10 watts is delivered (~0.091 Amperes).
  • Connect a 1 watt bulb and 1 watts is delivered (~0.0091 Amperes).
  • Connect no bulb and no watts are delivered (can you imagine all those electrons spilling on the floor? ;)
 


I wish I had my notes from November 2018 when I migrated one additional account from an older MacBook Pro with Thunderbolt 2 using the Apple adapter to Thunderbolt 3 for a brand new 2016 MacBook Pro. It was one of the slowest migrations that I have recently done. So the performance numbers you obtained using Thunderbolt between Apple machines are not a surprise.
 


Ric Ford

MacInTouch
I wish I had my notes from November 2018 when I migrated one additional account from an older MacBook Pro with Thunderbolt 2 using the Apple adapter to Thunderbolt 3 for a brand new 2016 MacBook Pro. It was one of the slowest migrations that I have recently done.
It was that exact scenario that first made me aware of the problem years ago. I had two MacBook Pros, each with an internal SSD, and I wanted to clone from one to the other. Naturally, Thunderbolt Target Disk Mode seemed like a great, fast option. But... it wasn't. It was stunningly slow, and that's when I began Thunderbolt Target Disk Mode. It has remained stunningly slow in the years since, through today.
 


Ric Ford

MacInTouch
I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:
Write: 895 MB/s​
Read: 468 MB/s​
That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).
I’d be interested to see your results if you connected them together by Thunderbolt networking and mount one as a network share (SMB and/or AFP) on the other. I believe you should be able to select a network volume for testing in Blackmagic Disk Speed Test.
I share Todd's curiosity about what numbers one might see from a Thunderbolt 3-connected "point to point" networked drive, served by a machine with a very fast SSD. It would have to be SMB, I think, but if the protocol implementations are highly tuned, it wouldn't completely surprise me if it were faster than target disk mode.
I spent more unsuccessful time yesterday trying to get this to work, and I have no idea what's wrong. Things I tried...
Unable so far to get Thunderbolt 3 file sharing working with the 2018 MacBook Pro (on the latest Mojave), I connected the 2017 iMac 5K (running macOS 10.12) and a 2017 MacBook Air (running macOS 10.13) via Apple's Thunderbolt 3-Thunderbolt 2 adapter, mounted a file-shared volume from the iMac on the MacBook Air, and ran Blackmagic Disk Speed Test. Results were extremely inconsistent (is this due to caching?), but I saw results like this for a file-shared volume over the Thunderbolt 2 network.

AFP:
Write: 150 MB/s​
Read: 621 MB/s​
SMB:
Write: 314 MB/s​
Read: 330 MB/s​
Here's what I get when using the iMac's internal flash drive directly:
Write: 2010 MB/s​
Read: 2286 MB/s​
Here's what I got over Thunderbolt 3 to a Samsung X5 SSD:
Write: 2033 MB/s​
Read: 2627 MB/s​
Here's what I got over Thunderbolt 2 to the Samsung X5 SSD:
Write: 1266 MB/s​
Read: 1293 MB/s​
Of course, Gigabit Ethernet is still worse than Thunderbolt networking:
Write: 75.6 MB/s​
Read: 71.6 MB/s​


#benchmarks
 


Ric Ford

MacInTouch
I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:
Write: 895 MB/s​
Read: 468 MB/s​
That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).
Unable so far to get Thunderbolt 3 file sharing working with the 2018 MacBook Pro (on the latest Mojave) ... I saw results like this for a file-shared volume over the Thunderbolt 2 network.

AFP:
Write: 150 MB/s​
Read: 621 MB/s​

SMB:
Write: 314 MB/s​
Read: 330 MB/s​
#benchmarks
OK, I did a clean install* of macOS Mojave onto an unencrypted volume on the 2018 MacBook Pro and was finally able to get Thunderbolt 3 networking to function, file-sharing from the 2017 iMac 5K.

Blackmagic Disk Speed Test had huge variability, but I got some results like these, varying from run to run:

AFP:
Write: 931 MB/s​
Read: 1086 MB/s​

SMB:
Write: 791 MB/s​
Read: 922 MB/s​



*actually a clone of the virgin Mojave system shipped on the 2017 iMac, ironically...
 


Ric Ford

MacInTouch
I just put a 2017 iMac 5K in Target Disk Mode and connected it over Thunderbolt 3 to a 2018 MacBook Pro. Blackmagic Disk Speed Test says:
Write: 895 MB/s​
Read: 468 MB/s​
That's an awful lot slower than the 40 Gbps (or even 22 Gbps) that Thunderbolt 3 should provide (i.e. ~3000 MB/s).
Time for Carbon Copy Cloner to clone a vanilla macOS Mojave partition from a 2018 MacBook Pro to an empty iMac 5K volume in Thunderbolt 3 Target Disk Mode:

29.2 GB in 5 min. 40 sec. (omitting subsequent startup cache update time at end) is about 86 MB/s if my math’s right.
 


Time for Carbon Copy Cloner to clone a vanilla macOS Mojave partition from 2018 MacBook Pro to iMac 5K in Thunderbolt 3 Target Disk Mode:
29.2 GB in 5 min. 40 sec. (omitting subsequent startup cache update time at end)
If the target drive was clean, the CCC (file copy) operations had essentially no seek delays and very little conversation between systems - [CCC] just keeps a stream going and going, one file after another. Doing a restore or migration most likely involves much additional overhead chatter. So, again, your results are not surprising.

Thanks for documenting all these test cases. I've seen many, but the desired end result was always good configurations, not shortest time, so I never made much note of the times involved, especially since, for the most part, they are better times than those achieved a decade or two ago.
 


Ever wonder why it is safe to connect an 85-Watt MacBook Pro power brick to an Air that needs only 45? Or how a 45-Watt MacBook Air charger might (eventually) top up a quiescent MacBook Pro?
Every power supply from every manufacturer works this way.

The spark from a short circuit is because a short circuit is, effectively, an infinite load. So it will drain everything the supply can produce (burning it out, if there is no current-limiting circuitry in place).

An 85W power supply may (and hopefully does) have a current-limiting circuit to prevent it from trying to deliver more than 85W - that will prevent it from overheating and burning out if it is overloaded (e.g. attaching it to a computer that's trying to draw 100W), but that would be completely unnecessary when attaching it to a lower-power device.

The power delivery protocols on USB are not designed to keep a power supply from forcing more current into a device than it can handle, they are designed to prevent the device from drawing more current than the cable can deliver without overheating.
 


... Connect no bulb, and no watts are delivered (can you imagine all those electrons spilling on the floor? ;)
James Thurber told this story:
My grandmother lived the latter years of her life in the horrible suspicion that electricity was dripping invisibly all over the house. It leaked, she contended, out of empty sockets if the wall switch had been left on. She would go around screwing in bulbs, and if they lighted up, she would fearfully turn off the wall switch and go back to her Pearson's or Everybody's, happy in the satisfaction that she had stopped not only a costly but dangerous leakage. Nothing could ever clear this up for her.
 


I have a 2017 MacBook Pro 15" that had the keyboard replaced when that recall went out. Because the top of the computer is one unit, it also includes the battery, so that was also replaced, but the USB-C/Thunderbolt assemblies, two on each side, were reattached to the motherboard and to the side of the computer with glue, I believe. They are not as solid as they once were, and 3 out of the 4 ports would fail regularly/intermittently.

I finally convinced Apple to take a look at it, even though we are out of warranty as I missed the 30-day cutoff to purchase Apple Care. A Genius person ran diagnostics and told me that the hardware was fine, the issue was in the software, and that the best solution would be to wipe the computer and replace everything manually - not to use a backup for migration - and then add each item in Documents back, and then reinstall all the software, one by one.

Frankly, I don't have the weeks that effort would take, and asked about modifying the preferences and extensions. He had little idea about that process but, with caution, thought it might work.

I went into the Libraries (all three) and removed items that had been around for more than a few years and were specific to peripherals and software that I no longer used. I was quite brutal about the culling, and even though I had to password-accept each deletion, I did remove several hundred older items.

Well, what do you know, the four ports are now working like a charm. I am also getting the speed back that I was missing in the file transfers, and things have been that much faster.

My advice is to take a look of the older preferences and delete them — that may be the cause of your slowdown. Worked for me.
 


Ric Ford

MacInTouch
... My advice is to take a look of the older preferences and delete them — that may be the cause of your slowdown. Worked for me.
That's a great story, but as far as my own test results are concerned, it's clearly irrelevant to the problem, since both the internal drive and all other external drives are working at top speed - the only thing that's slow is Target Disk Mode, and that's been true for many years and many tests on many different Macs and Mac operating systems.
 


Try this analogy: The AC outlet in a typical US home is a nominal 110 Volts AC - a "constant voltage source.”
  • Connect a 100 watt bulb and 100 watts is delivered (~0.91 Amperes).
  • Connect a 10 watt bulb and 10 watts is delivered (~0.091 Amperes).
No argument with that statement. But I have an inexpensive bedside swingarm lamp which is clearly labeled, "Caution: To Reduce the Risk of Fire Use MAX 40 Watt Type A." The lamp is dumb, and depends on humans using it to read and follow the instructions. Screw a 100-watt bulb into that lamp, and it will work, until it dangerously overheats.

On the electronics front, and by the kind of equipment, you'll understand this was some years ago, we were moving offices and our own maintenance crew plugged the power supply from a DSL modem into the input port for a then very expensive LinkSys WiFi router. Pffffft. The barrel plugs were identical, the power supplies looked the same....

The USB-C connector may just be a replacement plug for old-fashioned 500mA 5V 4.5W USB 2, or it can go all the way to USB 3.0 Power Delivery capability of 100 watts / 20 volts. "Power Delivery" is supposed to be "intelligent" with chips on each end that communicate to each other what level of power is safe and necessary. Bad programming, bad chips, bad cables, and it can go wrong.
Wikipedia said:
USB-C

... Many cables claiming to support USB-C are actually not compliant to the standard. Using these cables would have a potential consequence of damaging devices that they are connected to. There are reported cases of laptops being destroyed due to the use of non-compliant cables.

Some non-compliant cables ... (cause) a device connected to the cable to incorrectly determine the amount of power it is permitted to draw from the cable. ... Cables with this issue may not work properly with certain products, including Apple and Google products, and may even damage power sources such as chargers, hubs, or PC USB ports,
 


No argument with that statement. But I have an inexpensive bedside swingarm lamp which is clearly labeled, "Caution: To Reduce the Risk of Fire Use MAX 40 Watt Type A." The lamp is dumb, and depends on humans using it to read and follow the instructions. Screw a 100-watt bulb into that lamp, and it will work, until it dangerously overheats.

On the electronics front, and by the kind of equipment, you'll understand this was some years ago, we were moving offices and our own maintenance crew plugged the power supply from a DSL modem into the input port for a then very expensive LinkSys WiFi router. Pffffft. The barrel plugs were identical, the power supplies looked the same....

The USB-C connector may just be a replacement plug for old-fashioned 500mA 5V 4.5W USB 2, or it can go all the way to USB 3.0 Power Delivery capability of 100 watts / 20 volts. "Power Delivery" is supposed to be "intelligent" with chips on each end that communicate to each other what level of power is safe and necessary. Bad programming, bad chips, bad cables, and it can go wrong.
Or, to paraphrase all that ... using inappropriate or outside-of-specification equipment can be hazardous.

Since humans live by "If it fits, it is OK", hazards abound.
 


Just ran into the Mac Mini 2018 (6-core i7) problem where an unpowered device or hub (AmazonBasics USB 3.1 Type-C to 4-Port Aluminum Hub) randomly disconnects.

I was attempting to transfer a large number of multi-gigabyte files from one USB 3 hard drive to another. I got disconnected part way through 3 times... I then connected the drives directly to the Mini and the copy process had no issues.

Wasn't this a known issue that was to be fixed by Apple with an update ? (I'm running Mojave 10.14.5.)
 


Ric Ford

MacInTouch
Just ran into the Mac Mini 2018 (6-core i7) problem where an unpowered device or hub
(AmazonBasics USB 3.1 Type-C to 4-Port Aluminum Hub) randomly disconnects.
...
Wasn't this a known issue that was to be fixed by Apple with an update ? (I'm running Mojave 10.14.5.)
There were some USB bug fixes, but they may be different problems:
Apple said:
What's new in the updates for macOS Mojave

macOS 10.14.4
  • Improves the reliability of USB audio devices when used with MacBook Air, MacBook Pro, and Mac mini models introduced in 2018.
macOS Mojave 10.14.2 Update
  • Resolves an issue that prevents displays from working when connected to MacBook Pro models introduced in 2018, if certain third-party USB graphics devices are also connected.
More FYI about hubs
Apple said:
Using USB devices with your Mac
Hubs that conform to what is commonly referred to as the "2008 version 1 USB 3.0 specification" are supported.
Another potential problem is electrical interference, e.g. between cables or cables/hub or cables/drive/hub, etc. Changing cables and spacing and orientation may help. The high clock speed of USB 3 seems to create far more of these problems vs. slow USB 2.

Also... I'd be very reluctant to use an unpowered USB hub to host storage devices—that seems like it might be asking for trouble, especially with multiple devices attached.
 


Just ran into the Mac Mini 2018 (6-core i7) problem where an unpowered device or hub
(AmazonBasics USB 3.1 Type-C to 4-Port Aluminum Hub) randomly disconnects....
It's a lack of sufficient power. I don't recommend connecting bus-powered hard drives to a hub, even if it's a powered hub. I always connect them directly to the Mac.
 


It's a lack of sufficient power. I don't recommend connecting bus-powered hard drives to a hub, even if it's a powered hub. I always connect them directly to the Mac.
I, too, have had problems with unpowered or even powered USB hubs in the past.

Since I started using this Anker powered hub this year I’ve had no disconnects or any problems.

I attach up to 5 bus-powered USB 3 drives without any problems.

Bought on Amazon through Ric’s MacInTouch Amazon link, of course.
 


FWIW, I used to have disconnects of backup USB drives with a powered USB hub when I was using it with my 2010 Mac Mini running on an external (FireWire) drive but have not had them since upgrading to a 2018 Mac Mini last month and moving the USB drive to it (with the 2018 Mini running from its internal solid-state drive). So insufficient power sounds plausible to me.
 


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