How to TRIM/DISCARD a whole SSD partition on Linux?

Question

My partition /dev/sda3 on an SSD drive doesn't contain any filesystem, but it contains garbage. How do I do a TRIM/DISCARD operation on the whole partition?

Answer 1

If your version of util-linux is new enough (September 2012), there is actually a purpose-built tool, blkdiscard, that is the best way to do this:

sudo blkdiscard /dev/sda3

But if you need compatibility to older Linux distro versions, read on... There are cases where hdparm/wiper.sh refuse to touch a volume because it's not a partition, so we need something beyond that.

The most supported way I've found is to take advantage of the fact that Linux swap volumes support DISCARD when they are enabled. The wipefs on the end is there so the volume isn't recognized as swap later.

D=/dev/sda3 ; mkswap $D && swapon -d $D && swapoff $D && wipefs -o 0xff6 $D

This issues the DISCARD on the majority of the device.

Answer 2

I know this question is pretty old, but...

The simplest way to do this is to simply create an ext4 filesystem on the partition with a reasonably recent version of mkfs.ext4. The first thing this tool does is TRIM the entire partition. Once you've done that, you can overwrite the data it's created with whatever filesystem you desire.

(I've just done this to create a new vfat partition on an SD card, for example.)

Answer 3

hdparm --trim-sector-ranges is low level, it is supposed to talk directly to the SSD, so no dependency on the filesystem. What wiper.sh does is use filesystem specific programs to map free (filesystem) regions to (hardware) SSD sectors, them use hdparm to trim those.

Answering the question, you can use hdparm to trim that partition, but you should be very careful. The way to do it is obtaining the sector range used by the partition, then use hdparm on that sector range. Probably you'll need to pass multiple sector ranges, as each range for --trim-sector-ranges can have at maximum 65535 sectors.

fdisk -l can tell you the beginning and size of the partitions. Pay attention to the units in use by fdisk, and to the sector size of your SSD.

Example (my SSD):

Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048    39070079    19534016   83  Linux

To discard the space before this partition, I could trim 2047 (512 byte sized, on my SSD) sectors starting from sector 1: hdparm --trim-sector-ranges 1:2047. I can't trim starting from sector 0 because that is the MBR (dunno how it goes for GPT).

To discard the space used by the partition, I'd do hdparm --trim-sector-ranges 2048:65535 67583:65535 133118:65535 .... It can be scripted but I'm not going to write one now.

Also just to be sure: I'm not guaranteeing anything here, I may have miscalculated sectors, do a backup of everything before effectively using --trim-sector-ranges.

Note: if you trim the "empty" space before the first partition, like I showed, be sure to reinstall GRUB (or whatever boot loader you use) before rebooting, as GRUB stores part of it on "unused" sectors before the first partition. Don't know other bootloaders but I guess it may be the case, so take care.

Answer 4

You could have a look at the script wiper.sh included with the hdparm package. It uses the hdparm command --trim-sector-ranges to TRIM all empty sectors on a partition, at least if it contains an ext3/4 filesystem. Not sure if it works with unformatted partitions, but you could always temporarily format it with ext4.

Answer 5

blkdiscard can work on partitions, not just on whole drives. I tested it successfully on Fedora 20. I checked the sources of blkdiscard - it's a very simple program that knows nothing about partitions. I assume the kernel does the translation.

Be very careful, blkdiscard asks no questions and shows no progress information.

If blkdiscard is not available, use this script and feed its output to hdparm. First argument is the number of sectors to trim, the second is the first sector to trim.

#! /bin/sh
# List ranges for hdparm --trim-sector-ranges-stdin
: ${MAXSECT=65535}
test $# = 2 || { echo "Usage: trimlist sectors offset" >&2; exit 1; }
sectors=$1
pos=$2
while test $sectors -gt 0; do
    if test $sectors -gt $MAXSECT; then
            size=$MAXSECT
    else
            size=$sectors
    fi
    echo $pos:$size
    sectors=$(($sectors-$size))
    pos=$(($pos+$size))
done

Answer 6

For some reason on recent Ubuntu and Debian blkdiscard stopped accepting partitions as parameters, but only full device. I was using it previously thus was surprised and looking for other options.

I like proski answer but concept of calculating sector ranges is very unfriendly for me, thus I rewrote the script to provide start sector and end sector as parameters, to feed to hdparm trim command.

This approach allows simply read the output of fdisk -l for start and end positions, calculating simple as that just -1 for end sector if we take start sector of following partition or just +1 for start if we want to trim free space after last data partition.

Important note: I have noticed that trimming till the end of drive will corrupt second GPT copy, thus will require fdisk and write again for fix.

And of cause please make backup if you have any important data on drive you want to trim.

Here is my modified version of a script gen_trim.sh:

#!/bin/bash
# List ranges for hdparm --trim-sector-ranges-stdin
MAXSECT=65535
test $# = 2 || { echo "Usage: $0 offset last_sector" >&2; exit 1; }
pos=$1
lsector=$2
sectors=$(($lsector-$pos))
while [ $pos -lt $lsector ] ; do
if [ $sectors -gt $MAXSECT ] ; then
        size=$MAXSECT
else
        size=$sectors
fi

echo $pos:$size
sectors=$(($sectors-$size))
pos=$(($pos+$size))


done

Usage:

./gen_trim.sh start_sector end_sector | hdparm --please-destroy-my-drive --trim-sector-ranges-stdin /dev/sdX

example, I want to trim end of drive, free space after last partition:

fdisk -l /dev/sdb
Disk /dev/sdb: 1.86 TiB, 2048408248320 bytes, 4000797360 sectors
...
/dev/sdb4  209717248 3907029134 3697311887  1.7T Linux LVM

last partition sector=3907029134 thus start sector is 3907029135

and end sector is simply drive size in sectors: 4000797360

then script is:

./gen_trim.sh 3907029135 4000797360 | hdparm --please-destroy-my-drive --trim-sector-ranges-stdin /dev/sdX

where sdX is my ssd or nvme drive.