14.04 LTS Трим problem on an SSD

I own в Lenovo laptop with an M.2 NGFF slot. I удар в лунку в 128 Великобритания ZTC SSD card. This card is GPT partitioned and seen схвати sdb. I использовал it for the / which is EXT4 formated. Then I did в fresh install of Ubuntu 14.04LTS with/tmp and/var residing on the harddrive (sda).

I was surprised to see that the / was not mounted with trim enabled. So I added the discard option to the fstab mount command. But still, everytime I do в учебник trim, it gets many blocks to trim. I also modified the Cron trim рукописный шрифт in order to have the ZTC card checked but to не avail.

Question: What did I did wrong and how could I have this fixed?

root@eroot@espineux:~# fstrim -v /
/: 75904069632 bytes were trimmed
root@espineux:~# mount
/dev/sdb2 on / type ext4 (rw,errors=remount-ro,discard)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/cgroup type tmpfs (rw)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /sys/firmware/efi/efivars type efivarfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
....
/dev/sda7 on /tmp type ext4 (rw,errors=remount-ro)
/dev/sda4 on /home type ext4 (rw,errors=remount-ro)
/dev/sda8 on /var type ext4 (rw,errors=remount-ro)
/dev/sda1 on /boot/efi type vfat (rw)
.......
root@espineux:~# tune2fs -l /dev/sdb2
tune2fs 1.42.9 (4-Feb-2014)
Filesystem volume name:   <none>
Last mounted on:          /
Filesystem UUID:          7b2f1cb8-9a3a-4586-9a04-a4c4127f50aa
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index    filetype needs_recovery extent flex_bg sparse_super large_file huge_file   uninit_bg dir_nlink extra_isize
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              5234688
Block count:              20915968
Reserved block count:     1045798
Free blocks:              18531778
Free inodes:              4802146
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      1019
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Sun Jul  5 11:13:57 2015
Last mount time:          Thu Oct 29 03:35:43 2015
Last write time:          Thu Oct 29 03:35:43 2015
Mount count:              152
Maximum mount count:      -1
Last checked:             Sun Jul  5 11:13:57 2015
Check interval:           0 (<none>)
Lifetime writes:          1189 GB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:           256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      fba5200e-8dcd-4a78-b50f-8e5ecb516cf5
Journal backup:           inode blocks