Slow write speeds with APFS encryped external SSD

According to these benchmarks performances found here on APFS, APFS encrypted, HFS and HFS+ encrypted, your loss of nearly 40% may be surprising as you are writing and not reading.

Testing environment summary :

Hardware : 2017 MacBook Pro, 16 GB 2133 RAM

OS : macOS 10.13 High Sierra

Have you encrypted your already APFS formatted SSD to an APFS encrypted or have you completely reformated your APFS drive to an APFS encrypted ?

If you didn't reformat before your second performance speed test, this may be a cause.

Finally, if you did completely reformat your hard drive, this answer may be interesting :

Extremely slow write speed to encrypted external drive on Mavericks

Up to 40% drop is reasonable with the all the overhead of the encryption, it's not for free. However I have found out with the M1 airbook it is also drive dependant.

M1 airbook with a verified dongle (can push 100+ MB):

Transcend 1TB: unencryped 100-110 MB/s, encrypted: 40-70 MB/s
Seagate 5TB: unencryped 100-110 MB/s, encrypted: 15-20 MB/s

2015 macbook pro (without dongle):

Transcend 1TB: unencryped 100-110 MB/s, encrypted: 60-80 MB/s
Seagate 5TB: unencryped 100-110 MB/s, encrypted: 60-80 MB/s

As you can see the 2015 macbook trashes the M1 airbook here, but encryption is the key here, because if i create an unencrypted APFS volume, it's pushing 100-110 MB/s.

I noticed storagekitd using a lot of cpu on M1.

And I also managed to kernel panic M1 big sur just by connecting an external hard drive with Suspected bundle: com.apple.iokit.IOUSBHostFamily.

This panic has big chance of happening whenever the notebook goes to sleep too:

https://discussions.apple.com/thread/252421595

USB is very raw on M1. Let's hope all the panic backtraces I sent will make a difference.