Utility to TRIM unallocated space on drive

Question

I have a drive (SD card) with a few ext4 partitions but also some unallocated space. The fstrim utility can only work within a filesystem. Before I reinvent the wheel and write one, is there another utility that can TRIM the unallocated space (or that can TRIM an explicitly specified range)?

I can verify that the majority of the unallocated space on the device is not currently known to be free by the controller, as I've observed that, on this particular card, reads to trimmed space return 0's, but a scan of the device shows plenty of garbage data left over.

Edit: I am having an issue using hdparm. The example below discards the first sector, but I am seeing the same results regardless of the range I specify. fstrim has no issues on the device:

root@ubuntu:~# hdparm --please-destroy-my-drive --trim-sector-ranges 0:1 --verbose /dev/mmcblk0 

/dev/mmcblk0:
trimming 1 sectors from 1 ranges
outgoing cdb:  85 0d 06 00 01 00 01 00 00 00 00 00 00 40 06 00
outgoing_data:  
00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ioctl(fd,SG_IO): Invalid argument
FAILED: Invalid argument

I am investigating further but does anybody have any insight?

Answer 1

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.

---

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.

Answer 2

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.

Answer 3

Note about blkdiscard - it is VERY VERY dangerous and can be messy.

I got accident on test system when issuing command:

root@test:/home/test# fdisk -l /dev/nvme1n1
Device               Start        End    Sectors   Size Type
/dev/nvme1n1p1        2048    1101823    1099776   537M EFI System
/dev/nvme1n1p2     1134592    1658879     524288   256M Linux RAID
/dev/nvme1n1p3     1658880 1025658879 1024000000 488.3G Linux RAID    
root@test:/home/test# 
root@test:/home/test# blkdiscard /dev/nvme0n1
root@test:/home/test# fdisk -l /dev/nvme0n1
bash: /usr/sbin/fdisk: cannot execute binary file: Exec format error
root@test:/home/test# 
root@test:/home/test# fdisk -l /dev/nvme1n1
bash: /usr/sbin/fdisk: cannot execute binary file: Exec format error
root@test:/home/test# fdisk -l /dev/nvme1n1p1 
bash: /usr/sbin/fdisk: cannot execute binary file: Exec format error
root@test:/home/test# 
root@test:/home/test# fdisk 
bash: /usr/sbin/fdisk: cannot execute binary file: Exec format error

It did TRIM another drive!!! OS was installed on nvme1n1p1..3 and nvme0n1 was test drive.

Fortunately I had complete loss of test system, not big deal, but I feel obligation to share this publicly to warn you.

I think better approach is fstrim and set issue_discards = 1 in lvm.conf as mentioned by frostschutz

Edit 2024: Despite someone dislike this, I have 30 years of computer experience starting with ZX Spectrum as my first pc. I am sure that there can be issues and even bugs at OS level mapper, especially on locked partition map situation, or when computer changed boot priority to other efi partition, when efi is present on both disks and system fstab contains efi defined on another disk. There can be multiple scenarios, thus blkdiscard command should be used with EXTREME CAUTION and my big recommendation is fresh system boot (reboot) before using it. This command destroys data.