Utility to TRIM unallocated space on drive

If you have a recent enough version of util-linux, it contains the tool blkdiscard which is able to TRIM entire devices, or ranges within a device using --offset and --length options.

Please note: blkdiscard is dangerous, if you let it TRIM the wrong regions, your data is gone!

So you can figure out the unpartitioned (free) regions of your partition table and then TRIM them using this tool. For msdos and gpt partitions, parted provides the free regions like so:

# parted -m /dev/sda unit b print free | grep ':free;'
1:17408B:1048575B:1031168B:free;
1:64022904832B:64023240191B:335360B:free;

Add a loop to it...

while IFS=: read -ra FREE
do
    echo blkdiscard --offset ${FREE[1]%%B} --length ${FREE[3]%%B} /dev/sda
done < <(parted -m /dev/sda unit b print free | grep ':free;')

which prints

blkdiscard --offset 17408 --length 1031168 /dev/sda
blkdiscard --offset 64022904832 --length 335360 /dev/sda

Verify that this output is correct for you, add additional options if you like (verbose?), and finally remove the echo so it will be actually executed, and you should be set.

The second command of that example actually fails because the length is too small - it may be worth checking inside the loop, ignore regions smaller than 1MB as they're unlikely to be successfully trimmed.

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If you are using LVM instead of partitions, you can create a LV for the unoccupied space and trim that:

lvcreate -l100%FREE -n blkdiscard SSD-VG
blkdiscard -v /dev/SSD-VG/blkdiscard
lvremove SSD-VG/blkdiscard

If you set issue_discards = 1 in your lvm.conf, you can skip the blkdiscard call as LVM will issue the TRIM on lvremove by itself.

hdparm --trim-sector-ranges can trim a range. The man page warns to use it, so you better be sure you got the right range and syntax.

I think sending a trim for all data outside a partition would be dangerous, as there is some hidden data there sometimes like bootloader code or second partition tables. You'd need to know exaclty, which areas outside of partitions are really unused.