Encrypted external SSD showed significant performance issues on macOS.
Encrypted external SSD showed significant performance issues on macOS.
I possess two external 4Tb SSDs. I used them to save my memories, such as photos and videos. After buying them both were set up with Apple data protection and filled with archive files, about 1.4 Tb of media was stored. One drive stayed in a safe spot while the other was used for daily tasks and more files were added. After some time I performed a test and noticed the read/write speed was extremely slow. On a new drive and the one I kept separate, the speed over the Thunderbolt connection reached around 2000 Mb/s. However, the drive I used regularly showed only about 200Mb write and 100Mb read. I checked with another USB 3.2 enclosure but the speed remained the same. The other SSD with the same data functioned normally and the Thunderbolt setup worked well with another SSD too. Thus I concluded the SSD might be faulty. After returning it to Amazon, I wiped the data and tried it again. To my surprise, the speed returned to normal! In the 3.2 enclosure it was slower than Thunderbolt but still quite respectable at 900 Mb/s write and 1100 Mb/s read. Maybe I thought it was because the drive was almost empty. So I filled it with data, but the speed stayed high. Now I’m confused – could Apple encryption be affecting this? How could that happen?
Encrypting a drive does slow it down. There are many methods to secure a drive, each with its own trade-offs in speed. I usually don’t encrypt all my drives unless I need to; when I do, I use LUKS, which is the typical choice for most Linux systems. If not, I simply encrypt individual files with Veracrypt, which performs well.
Encryption could indeed affect performance, though the results were unusual. Both storage devices had encryption enabled. This likely reduced their read/write rates from 2200 to around 2000 Mb/s, but my actual experience was noticeably slower—about 10 to 20 times less efficient. My main thought is there might be an issue with Apple’s encryption implementation.