Arch Linux

drahnr

Member

Registered: 2011-03-14

Posts: 73

SSD, cryptsetup/luks, filesystem

There is a lot of information floating around regarding triming, filesystems (ext4, btrfs) and cryptsetup/luks. Does anyone know proper information about the current state. The wiki is outdated, the luks7cryptsetup mailinglists are missleading and partly conflicting in itself. The archwiki seems to be outdated on that topic.

So enlighten me please if anyone is capable of and has the proper knowledge.

Thank you very much!

Rezero

Member

From: US

Registered: 2010-02-25

Posts: 30

Re: SSD, cryptsetup/luks, filesystem

Hey drahnr, I have an encrypted partition on my laptop that does support trim. It holds two LVM volumes, both of which are ext4, and both of which are mounted with the discard flag.

dmesg | grep discard

[    8.506939] EXT4-fs (dm-1): re-mounted. Opts: discard
[    8.579250] EXT4-fs (dm-2): mounted filesystem with ordered data mode. Opts: discard

In Ubuntu kernels (2.38.??) it would refuse to enable discard, so I'm guessing support was included the 3.0 release. I imagine it should work for btrfs too. I hope this helps

thetrivialstuff

Member

Registered: 2006-05-10

Posts: 191

Re: SSD, cryptsetup/luks, filesystem

I've got a similar setup (also with discard enabled), but as I understand it, the TRIMs are not currently passed through the device-mapper layer. Wiki page says that's coming in kernel 3.1?

So while they are supported and the filesystem is issuing them, at the moment I don't think they're reaching the actual SSD underneath. There are also security implications to using TRIM with encrypted partitions, but they're relatively minor (i.e. if you encounter someone smart enough to threaten your encryption by analysing TRIMed block patterns, odds are said adversary is also smart enough to try the rubber hose).

~Felix.

drahnr

Member

Registered: 2011-03-14

Posts: 73

Re: SSD, cryptsetup/luks, filesystem

@thetrivialstuff: you have to enable it manually in kernel 3.1 due to your already pointed security implications. Though.. there should not be much of private data on the pure root disk (given you have secondary HDD for your data and replace /usr /home and alike with partitions/folders on that one).

As in the meantime since I posted this thread kernel 3.1 hit the repositories, I will give encrypted root with trim support (implicitly marking this as fixed, tough not solved).

Regards

Last edited by drahnr (2011-11-14 23:55:40)