Encrypted APFS SSD Drive very slow when connected to Studio Display

[Finch2000]

Hello,

I have a 16'' M1 Macbook Pro connected to my Studio Display. I bought a brand new Crucial X9Pro SSD with 2TB. The SSD came extFat formatted and I connected it to my Studio Display via USB-C to test transfer speed with Black Magic Disk Speed Test.

I got around 900 MB/s. Then after I formatted the drive with APFS encrypted transfer speed dropped significantly:

APFS encrypted on Studio Display, Test size 1TB:

APFS encrypted on Studio Display, Test size 2TB:

First I thought, that was due to encryption, but plugged directly into the Macbook Pro I got:

APFS encrypted on 16'' M1 Macbook Pro, Test size 1TB:

I became curious and reformatted the drive with APFS (not encrypted) and tested again:

APFS without encryption on 16'' M1 Macbook Pro, Test size 1TB:

APFS without encryption on Studio Display, Test size 1TB:

So I found, that the APFS formatted SSD has nearly the same speed when plugged directly into the Macbook Pro or into the Studio Display, roughly about 900 MB/s.

APFS encrypted the speed drops to 720MB/s write / 780 MB/s read when plugged into the Macbook. But when plugged into the connected Studio Display, speed drops down to 432 MB/s write / 530 MB/s read.

This is still a good result, but I wonder, why encryption has such an impact on the speed, if the SSD is plugged into the Studio Display, where transfer speeds are quite similar for unencrypted APFS.

I have similar speeds with encrypted APFS for a 1TB Samsung T7 and a 1TB Sundisk Extrem. ( I can not do unencrypted APFS benchmarks on those, since they are full with data, but I remember a similar drop in speed after formatting with encrypted APFS).

I've tested 2 different USB C cables (one that came with the drive and an other quality cable).

Any idea, what makes a SSD formatted with encrypted APFS so slow when it is connected to the Studio Display ?

Has anyone a higher transfer speed with encrypted APFS formatted SSD drives, that are connected to the StudioDisplay ?

 

[Fishrrman]

Do you really need the encryption feature?
(I understand that in some cases one does)

 

[Finch2000]

Hello, for safety I encrypt everything, especially external drives.
Normally the speed penalty is acceptable, but in combination with the Studio Display it is quite extreme.

 

[Coot42]

I see the exact same: 780MB/s or so when connected directly to the Mac, drops to 500MB/s when connected via Studio Display. I also have a 16” M1 Pro MacBook Pro, Studio Display, and the same 2TB Crucial X9 Pro external SSD formatted as encrypted AFPS.

It makes no sense to me, as presumably the Mac is doing the encryption/decryption.

Anyone have any ideas what is going on?

 

[PaulD-UK]

Usually when a display's USB-C ports don't achieve full bandwidth its because of limitations of the data bandwidth of the cable used to connect the display to the computer. The video bandwidth gets priority.

 

[Coot42]

Like the original post in this thread, I reformatted the SSD as regular APFS (i.e. not encrypted) and then I get the same, higher, speeds whether direct to the Mac or via the Studio Display - around 880MB/s.

So it does seem to be specific to encryption, which is what I don't understand at all because it's the Mac (I assume) that is doing the encryption/decryption and shouldn't be affected by the Studio Display?