Comment 1 for bug 1281587

note that the initramfs image does NOT support "allow_discards" at the moment. the script "scripts/local-top/cryptroot" only supports the "discard" option:

                discard)
                        cryptdiscard="yes"
                        ;;

furthermore, "allow_discards" is not copied into conf/conf.d/cryptroot
so, to avoid changing initrd and packages/infrastructure that generates it, ubuntu should use "discard" in /etc/crypttab.

a viable alternative is to change the default in the script/local-top/cryptroot script:

        # Defaults
        cryptcipher=aes-cbc-essiv:sha256
        cryptsize=256
        crypthash=ripemd160
        crypttarget=cryptroot
        cryptsource=""
        cryptlvm=""
        cryptkeyscript=""
        cryptkey="" # This is only used as an argument to an eventual keyscript
        crypttries=3
        cryptrootdev=""
        cryptdiscard=""
        CRYPTTAB_OPTIONS=""

by changing cryptdiscard to yes