SanDisk Extreme Portable SSD Not Getting Full 1050 MB/s over USB-C

[rm5]

I've had my 1 TB SanDisk Extreme Portable SSD for almost a year now, and it's been a great drive. However, there's one thing I've noticed when plugging the drive into the USB-C port on my USB 3.0/type C card on my Mac Pro—which is that it is getting substantially slower speeds than advertised. It's rated to get 1050 MB/s both ways, and for some reason it's only getting 500 MB/s, if even that. And this is when plugged into USB-C. When plugged into my M1 MacBook Air directly, it doesn't do much better—maybe gets 600 MB/s on that machine... so only 100 MB/s more than my 5,1 Mac Pro. Oh, and don't even get me started on USB-A - when it's plugged into the included USB-C>USB-A adapter, it gets no more than 350 MB/s over a USB 3.2 gen 2 connection.

Any ideas why this might be the case? It's formatted as APFS, with two volumes, one for files and another for TM backups. I've also run the speed tests "cold," so the cache is not full, etc. Screenshot from the 5,1 attached.

 

[mfram]

I have the 2TB version of that drive directly plugged into my 2020 MBP -- the last Intel version. I'm using the cable that came with the drive. I have the same drive setup, 2 APFS Volumes; I'm getting pretty much the same results.

 

[bogdanw]

Any ideas why this might be the case? It's formatted as APFS, with two volumes, one for files and another for TM backups.

APFS might be the problem. Have you run First Aid on the disk?
Unmount the volumes and follow Apple’s advice “Repair volumes, then containers, then disks”
https://support.apple.com/HT210898
https://support.apple.com/en-us/HT210898

 

[Fishrrman]

You NEVER get the full speeds for which a drive is rated.
You ALWAYS get "something less".

Assuming this is a USB3.1 gen2 drive, about 850-900MBps read speeds would be about "the best one could get".

For some reason, newer Macs with Apple Silicon aren't even doing that well (in most cases).