On Sun, Dec 20, 2020 at 12:47 PM Mistave <mistave@xxxxxxxxxxxxxxx> wrote:
Hello!
...
there is so much contradicting information available online. Some people
mentioned that a "discard" parameter should be added to /etc/crypttab
entry, others claim they must be present on both files - fstab and
crypttab. Some even suggest to add an "allow-discards" parameter to the
GRUB kernel command line in /etc/default/grub file. I was also told that
the continuous TRIM is discouraged and that periodic should be used instead.
What's the correct thing to do here?
There's a longer explanation e.g. here: https://stackoverflow.com/questions/61428311/ssd-trim-on-linux and I understand that LUKS does not allow TRIM by befault, because of security issues:
"Note that if you're using LVM or cryptsetup, all such layers need to
be configured to pass through the discard operation to the lower layer.
By default, cryptsetup ignores discard operations as it prioritizes
privacy over performance – TRIM by its nature reveals which disk areas
are in use and which ones are free."
For the last part I now think I understand the need for passing through discard operations to the lower layer (haven't done it but also haven't had problems in years using LUKS). I think something like this could be what you're looking for: https://blog.christophersmart.com/2013/06/05/trim-on-lvm-on-luks-on-ssd/ - I found several similar posts on google, it seems you basically need to ensure that discards are sent to the crypto layer by adding the allow-discards option to /etc/crypttab... Haven't actually done it myself - maybe I should do that in near future, sounds like a good idea...
Br,
M.
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