I went away for two hours and when I came back, my backups were about 10% done. I was puzzled; it should have taken at most 20 minutes.
Turns out, all three of the Samsung T5 2TB SSDs I plugged in are at USB 2.0 speeds, 20X slower than they ought to connect. On the LG 5K, no problem—they ran at full speed, as they also do when plugged into the Thunderbolt 3 ports on the 2019 Mac Pro. So obviously it’s not the fault of the three SSDs.
Witness, below, USB 2.0 speeds of 480 Mb/sec vs 10000 Mb/sec that should be in place. That is 21X too slow meaning horrible performance, slower than the slowest hard drive.
- Rebooted twice — USB 2.0.
- Unplugged and Replugged — USB 2.0.
- Unplug them all, plug one in — USB 2.0.
- Turned the air blue with profanity — USB 2.0.
There is a rule in life: “get the easy stuff right”. Apple seems to be clueless on that front. Here we have a $4999 display with a $999 stand and $499 AppleCare, plus tax on all that. Good thing the display is on loan and I didn’t buy it.
Slow performance is by design limitation
This behavior is BY DESIGN. Apparently the 6K display sucks up nearly all the available Thunderbolt 3 bandwidth so that the USB-C ports are good for charging/syncin. The 480 Mbps bandwidth for data transfer suits most Apple iOS products which still have those pathetically slow speeds—wireless is probably faster.
One Thunderbolt 3 (USB-C) port, three USB-C ports
One upstream port for Mac Pro or other Thunderbolt 3 host (96W host charging)
Three USB-C (USB 2) ports for charging or syncing(3)
(3) For the 16-inch MacBook Pro, USB-C ports have USB 3.1 Gen 1 data transfer speeds
Egads. It makes the Apple Pro Display XDR even more unattractive—useless as a hub as far as I’m concerned, it’s a dead-ended display. At 1/5 the price, the about $1299 LG 5K display is far more attractive since its USB-C ports run fast.
* $6500 with Apple Pro Stand and AppleCare and tax.