I bought an external SSD with a USB 3.1 gen 2 enclosure. I'm on macOS 10.13.6 with a MBP (late 2013).

Using APFS I get write speeds of around 390–405 MB/s. So far, so good. However formatting the drive to APFS (encrypted) results in way slower write speeds of around 250–260 MB/s.

Is such a performance loss of nearly 40% normal for an encrypted drive, or am I doing something wrong?

I used a 10GB test file and cp to measure the performance. Copying through Finder results in similar performance.

4 Answers 4


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

enter image description here

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

  • Hm, but according to those benchmarks only the read speeds of APFS encryped should be significantly slower compared to normal APFS. Write speed should be about the same…
    – YourMJK
    Sep 11, 2018 at 16:13
  • @M.J.K Indeed, I misunderstood your question. I have edited my answer with a possible answer : Have you encrypted your already APFS formatted SSD to an APFS encrypted or have you completely reformated your APFS to an APFS encrypted ? If you didn't reformat before your second performance speed test, this may be a cause.
    – JKHA
    Sep 11, 2018 at 18:56
  • I completely reformatted the drive. I also tried encrypting the already APFS formatted drive but there wasn't any difference. So this shouldn't be the issue.
    – YourMJK
    Sep 11, 2018 at 19:03
  • 1
    @M.J.K, ok, I edited a final time my answer and giving you an other Apple StackExchange link with a similar question of your and its answer. I know it's not a completely full answer and I hope the community will help, as it surpasses my knowledges !
    – JKHA
    Sep 11, 2018 at 19:12
  • 1
    Ok, I understand, have you tried to benchmark speed writing performance with HFS instead of APFS ? In case the performance with HFS are better, here are the pros and cons of HFS and APFS : techrepublic.com/article/…
    – JKHA
    Sep 11, 2018 at 20:06

The problem still exists with a MacBook Pro 2020 running macOS BigSur.

I am using a 2 TB SSD with an USB 3.1 enclosure. The SSD manufacture (Crucial) mentions read / write speeds from 560/510 MB/s in their product information. Tested with several cables and on different ports.

Get around 400/450 MB/s with APFS: enter image description here

Get around 200 MB/s with APFS encrypted: enter image description here

Thats a ~ 50 % difference!

After talking with the Apple Care support they told me that encrypted file formats shouldn't have a huge effect on read / write speed (but as we can see, they do have an effect). They solved a similar problem with another customer by changing the format to the old Mac OS Extended (Journaled) one. They have also advised me to ask the SSD manufacture for additional information and help.


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:


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


I see a drops of 17% (write) and 25% (read) when using encrypted vs non encrypted (One APFS container with APFS Volumes).

It seems that the 40% drop you experience is high in comparison, but it is hard to tell with so little data.

APFS Volume type | Write (MB/s) | Read (MB/s)
apfs | 912 | 919
apfs encrypted | 756 | 688

Using case-sensitive or not made difference.


  • OS: MacOS 10.14.6 Mojave
  • Hardware: Macbook Pro 2017, 16 GB 2133 MHz LPDDR3 and 2.5 GHz Intel Core i7
  • SSD: samsumg 970 evo NVMe M.2
  • External enclosure: sabrent usb 3.1 enclosure for NVMe PCIe M Key M.2 ssd.

APFS speeds apfs speeds

APFS encrypted speeds apfs encrypted speeds

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