From: Mistave <mistave@countermail.com>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] Properly enabling TRIM for dm-crypt on an SSD
Date: Mon, 21 Dec 2020 17:53:48 +0100 [thread overview]
Message-ID: <3c92603c-2254-ede4-d454-a949ec2928eb@countermail.com> (raw)
In-Reply-To: <CAJN12jm-KqRWA8qFwygp7NvcvVGR_t9HV2o54QO3fUHUh4SEmw@mail.gmail.com>
On 2020-12-20 19:12, Martin Jørgensen wrote:
> *"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."*
So, if I understand correctly, this means that even though the fstrim
utility runs every once in a while and sends TRIM commands down the
pipe, they will be caught and stopped by the dm-crypt layer unless it is
also configured to let them pass.
In this case the only thing I need to do is activate TRIM on dm-crypt
since I don't use LVM.
> 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...
The /etc/crypttab should use the keyword "discard" according to debian
documentation. I believe that "allow-discards" is meant to be a kernel
parameter passed by the bootloader. I've also seen
"rd.luks.allow-discards" or "rd.luks.options=discard" used on some
pages. We'll see, if any work for me.
To test, I'm going to use the following command:
# dmsetup table | grep allow_discards
Kind regards,
M.
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next prev parent reply other threads:[~2020-12-21 16:54 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-20 11:36 [dm-crypt] Properly enabling TRIM for dm-crypt on an SSD Mistave
2020-12-20 18:12 ` Martin Jørgensen
2020-12-21 16:53 ` Mistave [this message]
2020-12-21 21:45 ` Mistave
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