Encrypted external SSD became very slow (macOS)

[Aleksey]

I have two external 4Tb SSDs. I was using it to store my memories, like photos, videos, etc. After the purchase both were initialized with Apple data encryption and filled with archive data, approximately 1.4 Tb of media files. One drive I kept in a secure place and the other I used for everyday work and kept adding files. After some time I run a test and realized that the read/write speed was incredibly slow. On a new drive and the one I kept separate, the read/write speed over the Thunderbolt connection was ~2000 Mb/s. But the one that I kept using from time to time, showed me ~200Mb write an ~100Mb read. I tested this using a different, USB 3.2 enclosure, but the speed was the same. The other SSD with the same data kept working as expected and the Thunderbolt enclosure was also working great with another SSD. So I decided the SSD was faulty. After filing for a return with Amazon, I erased the data and just in case, decided to test it one last time. To my surprise the read/write speed returned back to normal! In the 3.2 enclosure, it was less, than in the Thunderbolt, but still very respectable 900 Mb/s write and 1100 Mb/s read. OK, I thought, surely this is because the drive is nearly empty now. So I filled it with data, but nothing changed - the speed was still great.

 

Now I do not understand - can Apple encryption be the cause of this issue? How can this be?

[Aleks NE]

Yeah, encrypting a drive makes it slower. There are various ways of encrypting a drive; with various performance sacrifices. I personally rarely encrypt my entire drives, if I do, I do so with LUKS as that's the standard on most Linux distros. Otherwise, I just encrypt the files with Veracrypt which works pretty well. 

[Aleksey]

2 hours ago, Aleks NE said:

Yeah, encrypting a drive makes it slower. There are various ways of encrypting a drive; with various performance sacrifices. I personally rarely encrypt my entire drives, if I do, I do so with LUKS as that's the standard on most Linux distros. Otherwise, I just encrypt the files with Veracrypt which works pretty well. 

Yes, encryption may slowdown read/write speed, but what I observed was something extraordinary. Both drives were encrypted. This probably slows down the read/write speed from 2200 to 2000 Mb/s, but the speed that I consistently observed in my case was like 10-20 times slower. All I can think of is that there is some bug in the Apple encryption software.