I have a 128GB Somnambulist SSD. I know this brand is one of the worst. I measured the speed using GNOME Disk Utility, and it showed a read/write speed of 420/340.

After encrypting the SSD with Debian 12, the read speed, as measured by the GNOME Disk Utility, dropped to 13.5 MB/s!

Is this drop in speed normal, or is the issue likely related to the SSD itself?

  • Is there any chance the disk supports OPAL? It's a pretty common feature in SSDs. sedutil-cli --scan should tell you. I'm not sure how normal distro's set up a PBA to unlock it these days.
    – davolfman
    Jun 19, 2023 at 22:50

1 Answer 1


If your CPU is old enough it may not support AES-NI instructions, so encryption/decryption will be slow.

grep -qw aes /proc/cpuinfo && echo Supported || echo Unsupported

Will tell you everything.

  • 3
    Intel Atom N270: unsupported. Thank you very much.
    – Daniel
    Jun 19, 2023 at 15:12
  • 8
    @Daniel if you must use encryption, you could try your luck with another cipher, like serpent-xts - it might be slightly faster than the default aes-xts on this cpu (try cryptsetup benchmark, but also benchmark with real I/O). Jun 19, 2023 at 16:10
  • 3
    @Daniel Hmmm, I tried this with an old version of Lubuntu earlier, where benchmark showed faster-than-aes speeds for serpent-xts (>20MB/s instead of >10MB/s); but in Debian 12 the benchmark seems to be about the same for all ciphers. Sorry, I rarely / never use this device anymore (MSI netbook with N270), only dusted it off the shelf today... it's 15 years old and was very low end even back then, so it's just that slow unfortunately Jun 19, 2023 at 18:17
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    @Daniel You may want to try using something other than BTRFS here, I strongly suspect that you will see significantly better performance. BTRFS is very write-heavy compared to XFS, ext4, or even F2FS, so performance limitations in the lower layers of the storage st6ackt end to have a much bigger impact for it. Also, if you really want encryption, try using cryptsetup benchmark to see what encryption modes perform best on your setup. You pretty much always want XTS for FDE usage, but but any of the XTS algorithms should be sufficient for your use case. Jun 20, 2023 at 0:18
  • 2
    @Daniel, if you want to use encryption, you might try the XTEA cipher (you may need to compile a custom kernel to get support for it). It sacrifices security for performance, but it's better than nothing.
    – Mark
    Jun 20, 2023 at 2:27

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