Because I (taggart) keep forgetting, I am creating this page to track the details about TRIM / DISCARD support.
DISCARD support for dmcrypt was added to Linux in 3.1.
Support in the dmcrypt tools was added in 1.4.x
The linux commit
commit 772ae5f54d69c38a5e3c4352c5fdbdaff141af21 Author: Milan Broz <email@example.com> Date: Tue Aug 2 12:32:08 2011 +0100 dm crypt: optionally support discard requests Add optional parameter field to dmcrypt table and support "allow_discards" option. Discard requests bypass crypt queue processing. Bio is simple remapped to underlying device. Note that discard will be never enabled by default because of security consequences. It is up to the administrator to enable it for encrypted devices. (Note that userspace cryptsetup does not understand new optional parameters yet. Support for this will come later. Until then, you should use 'dmsetup' to enable and disable this.)
- page detailing the implications of enabling TRIM on a dmcrypt device (by the author of the above commit)
- How to enable it
- some howtos