I agree that "issue_discards = 1" should become the default in lvm on Debian.
There is a case where you might not want TRIM/discards, there are security implications to enabling it with dm-crypt. In the commit message which added this support, the author states: Note that discard will be never enabled by default because of security consequences, it is up to administrator to enable it for encrypted devices. and in the added documentation: WARNING: allowing discard on encrypted device has serious irreversible security consequences, discarded blocks can be easily located on device later. This can lead to leak of information from ciphertext device (unique pattern for detecting filesystem type, used space etc). https://www.redhat.com/archives/dm-devel/2011-July/msg00042.html But if I understand it correctly, as long as dm-crypt defaults to not enabling it, it would still be fine if LVM did have it enabled, you just wouldn't have it all the way down the stack to the hardware and would lose the benefit but still be safe. It might be worth documenting that, something like: The option "issue_discards" is enabled by default on LVM in Debian. Note that in order to get the benefits of discard, it needs to be enabled in each block layer down to the actual hardware. Due to security implications, discard is disabled by default in dm-crypt, so if you are using that you should first consult the dm-crypt documentation to understand the implications before enabling. Sound ok? -- Matt Taggart tagg...@debian.org
