I have a Raspberry Pi4 (4GB) with a 250GB SSD connected via USB3. The SSD has a write speed of about 70MB/s, which is very nice. The SSD is mounted via fstab and the following settings:

LABEL=DATA /media/extStorage   exfat-fuse nofail,auto,sync,gid=www-data,rw,umask=007 0 0

But I have a VeraCrypt encrypted file container which is about 95% of the SSD volume size. When I mount the container with the command

sudo -u root veracrypt /media/extStorage/data.hc /mnt/data/ --pim=230 -k "" --protect-hidden=no --fs-options "gid=www-data,umask=007"

the write speed is only about 3MB/s, which is 1/18th of the originally speed... When mounted and while writing the process "/sbin/mount.exfat-fuse /dev/sda1 ..." has a very high CPU usage: CPU usage while mounted and write operation

The command lsof for /media/extStorage shows that only VeraCrypt is accessing.

As far as I understand VeraCrypt, the CPU load should not be that high after mounting... I also tried using a much lower PIM, which was only faster when mounting.

So do I do somthing wrong when mounting the drive or the encrypted container (e.g. wrong or mising commands)? What could cause that kind of problems?

Thank you in advance for your answers.

EDIT: Just to mention: I downloaded the source code of VeraCrypt and compiled it myself on my Raspberry, if that could include an error...

I found that may the lack of a hardware AES module could be the problem... so the Raspberry have to use software AES which is CPU intense and therefore slower... I don't know how to solve this problem, because the RPi does not seem to have that module on the chip... (https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=207888&p=1568740&hilit=aes#p1568740) I never had that kind of problems before, because my Notebook and my Tablet support hardware AES. Maybe another encryption software (like dm-crypt) is more convenient?

EDIT2: This problem was solved by using EXT4 formatting instead of exfat. See my first comment under the first answer.

  • 2
    I can't read the text on the picture. Please don't use pictures of text. Instead paste the text direct into the question.
    – Ingo
    Nov 21, 2019 at 10:54
  • It says that the PID 274 with the user root uses 100% of a single CPU core with the command "/sbin/mount.exfat-fuse /dev/sda1 /media/data -o rw,sync,gid=33,umask=007".
    – Florian
    Nov 22, 2019 at 7:36
  • @Florian Your post refers to /media/storage, your comment says /media/data and the screenshot states /media/extStorage. Are you sure you have mounted the right file? Nov 22, 2019 at 8:46
  • 1
    Yes the paths are absolutely right. I am sorry for the confusion. To clearify: /media/extStorage is the mountpoint for the USB drive, /mnt/data is the mountpoint for VeraCrypt. I changed the OP...
    – Florian
    Nov 22, 2019 at 9:33
  • Can you run the benchmark of the encryption algorithm you're using and add the number to your post? Nov 22, 2019 at 10:10

1 Answer 1


I just have tried to write to an encrypted volume: TrueCrypt, AES encryption, the container is a partition on a USB3 drive, encrypted drive formatted as EXT4. I see a data rates between 45 and 52 MB/s (according to my file manager), with CPU load hovering around 65%: about 30% used by TrueCrypt and another 30% used by USB XHCI driver.

My TrueCrypt encryption benchmark (with 50MB RAM buffers) reports 121 MB/s encryption speed and 117 MB/s decryption speed for AES. As in your case, AES hardware support is N/A.

My advice would be that you try different encryption algorithms, e.g. Twofish. Perhaps AES encryption implemented in VeraCrypt performs poorly on RPi hardware. Or try a different encryption software.

PS. I assume that your RPi 4 is not throttled due to overheat or low power supply voltage. For instance, if I power my RPi by 4.8V instead of 5, the data rate drops from 52 MB/s to 12.

  • 1
    Thank you very much for your effort! The voltage topic seems to be very relevant for me, I measured down to 4.7V when the CPU is on full run. I consider to buy a new power supply... I also had success with different mount options: now I use the following options to mount my ext4 formatted drive: LABEL=EXTSTORAGE /media/extStorage ext4 nofail,defaults 0 0 and my VC mount options are veracrypt /media/extStorage/data.hc /mnt/data/ -k "" --protect-hidden=no -> now I have 45MB/s write speed which is very nice!
    – Florian
    Nov 24, 2019 at 13:10
  • @Florian So, you have changed the format of the disc containing the encrypted container file from exFAT to EXT4? I would expect some performance improvement, but not 15-fold. I also have exFAT SD cards, and the RPi 4 writes them as fast as the card can go (which is around 25-30 MB/s) Nov 24, 2019 at 16:05
  • Yes I changed that and the mount options of the USB drive itself (removed "auto,sync,gid=www-data,rw,umask=007" while mounting and replaced it with "default"). Only that doubled or trippled the write speed! And the removed mount-permissions (command "--fs-options") from VC did the rest. I did add these permissions because exFAT doesn't support permissions so I had to do a Workaround which seems to need a lot of CPU power I guess... Now I am losing about 20-25% of the write speed because of encryption and while writing the CPU load is about 50%. So that's good enough for my applications.
    – Florian
    Nov 25, 2019 at 10:04
  • @Florian Now that you mentioned it, I see you have used sync. This is a known performance killer in Linux and there are very few reasons to use it. If you want to make sure you don't lose any data, use a journal (that has a performance penality too, but not as bad as sync). Nov 25, 2019 at 10:28
  • 1
    Oh I didn't know that and I don't even know why I used that option. But now it's working fine so I will use the default options...
    – Florian
    Nov 26, 2019 at 12:03

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