Fix SSD Trim on Ubuntu 14.04 LTS

In Ubuntu 14.04 LTS SSD Trim is enabled by default.
That's nice and all, so I thought, nothing to do here but I found out
it doesn't work when you use LUKS crypt partitions, it's a bug.

Here the steps to fix it, please make backups of important files before
doing this!!
Note it only runs on Intel and Samsung SSD drives, see bottom of page
why.

First check if you have the same problems as me:

$ sudo fstrim /
fstrim: /: FITRIM ioctl failed: Inappropriate ioctl for device

Check what dmsetup gives:

$ sudo dmsetup table 
sda5_crypt: 0 233934848 crypt aes-xts-plain64 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0 8:5 4096 1

The reason for above error is the missing 'allow_discards' at the end.

How to fix, open this file:

$ sudo vi /usr/share/initramfs-tools/scripts/local-top/cryptroot

        cryptrootdev=""
        cryptdiscard=""
        CRYPTTAB_OPTIONS=""

Change cryptdiscard value to:

        cryptdiscard="yes"

Write changes to your initrd:

$ sudo update-initramfs -u
$ sudo reboot

Check:

$ sudo dmsetup table
[sudo] password for ron: 
sda5_crypt: 0 233934848 crypt aes-xts-plain64 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0 8:5 4096 1 allow_discards

You can also check if SSD trim is enabled by using lsblk:

$ lsblk -D
NAME                           DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda                                   0      512B       2G         0
├─sda1                                0      512B       2G         0
├─sda2                                0      512B       2G         0
└─sda5                                0      512B       2G         0
  └─sda5_crypt (dm-0)                 0      512B       2G         0
    ├─ubuntu--vg-root (dm-1)          0      512B       2G         0
    └─ubuntu--vg-swap_1 (dm-2)        0      512B       2G         0
sdb                                   0      512B       2G         0

If both values DISC-GRAN and DISC-MAX are >0, it's fine.

Now run fstrim again, please note that because it never worked on my SSD
it run >10 minutes to catch up, running it again took 35 seconds ;-)

$ sudo fstrim -v /
/: 72480993280 bytes were trimmed

Wow that's 67.5GB while the drive is 120GB total.

[    1.395347] ata1.00: ATA-9: INTEL SSDSC2CW120A3, 400i, max UDMA/133
[    1.405488] scsi 0:0:0:0: Direct-Access     ATA      INTEL SSDSC2CW12 400i PQ: 0 ANSI: 5

Ubuntu 14.04 has a default configured weekly crontab job which starts
'fstrim-all', so I leave it like this.

There is a warning inside the cronjob file btw:

$ sudo tail -n 6 /etc/cron.weekly/fstrim

# This only runs on Intel and Samsung SSDs by default, as some SSDs with faulty
# firmware may encounter data loss problems when running fstrim under high I/O
# load (e. g.  https://launchpad.net/bugs/1259829). You can append the
# --no-model-check option here to disable the vendor check and run fstrim on
# all SSD drives.
exec fstrim-all