SSDs have sophisticated wear-leveling algorithms which need to know about free blocks to work correctly [1]. Widespread Linux filesystems (e.g. Ext4, XFS, Btrfs) support to issue the needed commands automatically after removing data by adding the discard mount option but doing so can have a negative effect on performance [2], [3].

To read more about SSD handling in Linux see the help pages of your distribution (e.g. Arch Linux, Debian, Fedora, SUSE Linux).

This script does currently do two things:

• Run fstrim on all mounted filesystems that reside on block devices supporting discards.
  This does not check if the actual file system supports discard.
• Run blkdiscard on any free discardable space covered by LVM.
  It does so by creating temporary volumes covering 100% of the free VG space and issuing blkdiscard on them.

You need to have fstrim and blkdiscard (as well as all other support utilities used such as lvm and blockdev) available for execution. Besides that, the file systems as well as all block layers beneath them (e.g. LVM, dm-crypt) need to be configured to pass the trim commands on to the next layer. Of course it does only make sense to use discard-everything.sh if you don't mount your filesystems with the discard option.

Make sure you have issue_discards = 1 in the devices section of your lvm.conf (see [4] or your local manpage: man lvm.conf).

For devices created by crypttab add allow-discards as optional argument [5].
For those created by cryptsetup use the --allow-discards parameter (see [6] or your local manpage: man cryptsetup).

Just copy discard-everything.sh into /etc/cron.weekly/ or a similar place, or execute it manually regularly (as root).