TB4 and TB3 NVMe SSDs working at very low speed

Things to check:

-With the OWC unit plugged in and configured, open Utilities->System Information and look at Hardware->Thunderbolt/USB4 and see what is listed for the OWC device.

-Try uninstalling SoftRaid and test the OWC drives as individual drives. Based on the foot notes on the OWC product page:

1. "Maximum single drive performance is 817 MB/s Reads and 711MB/s Writes due to the bandwidth of the 1X PCIe3.0 bus."

See what the drives "base" performance is in the enclosure compared to those numbers.

-Try plugging a display or non-TB device into an adjacent TB port and then retest.

-If the individual drive tests seem reasonable based on the spec, then try re-installing SoftRaid. If the issue is still the same, then there could be a compatibility issue with SoftRaid.

In terms of USB-C speeds, there were issues on the M1s due to a "single lane" vs. "dual lane" USB 3.1 and 3.2 and appeared that the Macs only supported the single lane. So, example, Samsung T7 claim greater than 10 Gb/s but that is only with "dual lane" and "single lane" is half that. Whether the same issue continues to exist in in the Studio remains to be seen.

The alternative, to talk to Apple support first responder and 'jump through all the hoops" to eventually be told, "not an Apple Product" is not very appealing.

OWC sold you stuff, they know why it works the way it does, and they have somebody who can explain it. Contacting them is the practical solution.

Just for reference here is my data on my Mac Mini M1 and my MBA M1:

using WD Black SN750 in a USB 3.2 gen 2 enclosure I see speeds of 600/700 (write/read)

using WD Black SN750 in a TB enclosure I see speeds of 2400/2600 (write/read)

With your WD SN850 you should be seeing higher speeds but I do not believe it is the issue with the TB ports unless the Studio model has some issue or your enclosure is at fault. My TB enclosures are Trebleet and Acasis

I'm seeing different, but probably related issues. Just got the Mac Studio with the M1 Ultra. I have an OWC 4M2 and initially I had all sorts of problems until I realized one of the NVMe drives was dead. Now it's mostly works ok, though I have had it randomly not respond. I only have a 2 drive WD SN750 RAID1 in there, but I tested and it wrote a big file at 1.4GB/s, so speed seems to be fine. And more recently, I've been seeing my other NVMe enclosure stop responding. It's a 3rd party single NVMe on USB 3.1 connected to a TB4 port with a TB3 cable. I basically just use that as a big flash drive. For the record, all of this stuff works totally fine with my i9 MBP and I've had zero issues there - even with the dead drive in the 4M2.

Oh and I do have 2 displays hooked up via the 4M2. One on DP and the other on USB-C/TB. No issues with those.

OWC prides themselves on their support. They made money on your purchase. They have a deep stable of people with expertise on issues like this.

CALL THEM.

Can't help you with that speed problem. I have the Ultra and connect a Sonnet EchoExpress SE llle with OWC Accelsier 1A PCie card. WD NVMe 1000 1895 write and 2508 read The sonnet is connected directly to the Studio Ultra thunderbolt back port.

Its very quiet. Holds three PCie cards.

https://www.sonnettech.com/home.html scroll down to the video explanation of thunderbolt 4 demystified.