Testing TRIM for SSDs on Linux

There is a way to test it answered at unix.stackexchange.com by frostschutz (this answer is his merit so thanks him), copied below:

"Create a test file: (not random on purpose)

# yes | dd iflag=fullblock bs=1M count=1 of=trim.test
Get the address: (exact command may have to differ depending on filefrag version)

# filefrag -s -v trim.test
File size of trim.test is 1048576 (256 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0    34048             256 eof
trim.test: 1 extent found
Get the device:

# df trim.test
/dev/mapper/something  32896880 11722824  20838512   37% /
With this set up, you have a file trim.test filles with yes-pattern on /dev/mapper/something at address 34048 with length of 256 blocks of 4096 bytes.

Reading that from the device directly should produce the yes-pattern:

# dd bs=4096 skip=34048 count=256 if=/dev/mapper/something | hexdump -C
00000000  79 0a 79 0a 79 0a 79 0a  79 0a 79 0a 79 0a 79 0a  |y.y.y.y.y.y.y.y.|
*
00100000
If TRIM is enabled, this pattern should change when you delete the file. Note that caches need to be dropped also, otherwise dd will not re-read the data from disk.

# rm trim.test
# sync
# fstrim -v /mount/point/ # when not using 'discard' mount option
# echo 1 > /proc/sys/vm/drop_caches
# dd bs=4096 skip=34048 count=256 if=/dev/mapper/something | hexdump -C
On most SSD that would result in a zero pattern:

00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00100000
If encryption is involved, you will see a random pattern instead:

00000000  1f c9 55 7d 07 15 00 d1  4a 1c 41 1a 43 84 15 c0  |..U}....J.A.C...|
00000010  24 35 37 fe 05 f7 43 93  1e f4 3c cc d8 83 44 ad  |$57...C...<...D.|
00000020  46 80 c2 26 13 06 dc 20  7e 22 e4 94 21 7c 8b 2c  |F..&... ~"..!|.,|
That's because physically trimmed, the crypto layer reads zeroes and decrypts those zeroes to "random" data.

If the yes-pattern persists, most likely no trimming has been done."

This is my automated script:

#!/bin/bash
#
# This script is provided "as is" without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability, fitness for a particular purpose, or non-infringement.
#
# License GPL2
#
# by desgua 2014/04/29

function CLEAN {
cd "$pasta"
[ -f test-trim-by-desgua ] && rm test-trim-by-desgua && echo "Temp file removed"
echo "Goodbye"
exit 0
}

trap 'echo ; echo "Aborted." ; CLEAN; echo ; exit 0' INT HUP

if [[ "$(echo $USER)" != "root" ]]; then

read -n 1 -p 'Become root? [Y/n]' a
    if [[ $a == "Y" || $a == "y" || $a == "" ]]; then
        sudo $0 $1
        exit 0
    else
        echo "
        This script needs root privilege.
        "
        exit 1

    fi

fi


name=$(echo $0 | sed 's/.*\///')
if [ $# -ne 1 ]; then

echo "
Usage: $name /folder/to/test/

"
exit 1
fi

pasta=$1

read -n 1 -p 'Use fstrim? [y/N]' a
if [[ $a == "Y" || $a == "y" ]]; then
    fs=1
fi

method=
while [[ "$method" != "1" && "$method" != "2" ]]; do
read -n 1 -s -p 'Choose a method:
[1] hdparm (will fail in LUKS on LVM)
[2] filefrag (warning: you may have to force quit - close the terminal - in some cases of success trim if you see an output that never ends)
' method
done

function SDATEST {
disk=$(fdisk -l | grep /dev/sda)
if [ "$disk" == "" ]; then
echo "
fdisk did not found /dev/sda
"
exit 1
fi
}

function TEST {
echo "Entrying /" ; echo
cd $pasta
echo "Creating the file test-trim-by-desgua at $pasta" ; echo
dd if=/dev/urandom of=test-trim-by-desgua count=10 bs=512k
echo "Syncing and sleeping 2 seconds." ; echo
sync
sleep 2

hdparm --fibmap test-trim-by-desgua
lbab=$(hdparm --fibmap test-trim-by-desgua | tail -n1 | awk '{ print $2 }')

echo "As you can see, the file was created and its LBA begins at $lbab" ; echo

echo "Syncing and sleeping 2 seconds." ; echo
sync
sleep 2

echo "Removing file test-trim-by-desgua" ; echo
rm test-trim-by-desgua

trap 'echo ; echo ; echo "Aborted." ; echo ; exit 0' INT
echo "Syncing and sleeping 2 seconds." ; echo
sync
sleep 2

if [[ "$fs" == "1" ]]; then
    echo "fstrim $pasta && sleep 2" ; echo
    fstrim $pasta
    sleep 2
fi

echo "This is readed from sector $lbab: "
hdparm --read-sector $lbab /dev/sda

pass=$(hdparm --read-sector $lbab /dev/sda | grep "0000 0000 0000 0000")

if [[ $pass == "" ]]; then
    echo "
Trim failed...
You should see only 0000 0000 0000 0000 ...
"
else
    echo "Success!!!"
fi
exit 0

}

function LUKSTEST {
# Reference: https://unix.stackexchange.com/questions/85865/trim-with-lvm-and-dm-crypt#
echo 1 > /proc/sys/vm/drop_caches
cd $pasta
echo "Creating a \"yes\" file."
yes | dd iflag=fullblock bs=1M count=1 of=test-trim-by-desgua

#position=`filefrag -s -v test-trim-by-desgua | grep "eof" | awk '{ print $3 }'`
position=`filefrag -s -v test-trim-by-desgua | grep "eof" | sed 's| ||g ; s|.*255:|| ; s|\.\..*||'`
[[ "$position" == "" ]] && echo "Could not find the position of the file. Are you on a LUKS on LVM?" && CLEAN;

device=`df test-trim-by-desgua | grep "dev/" | awk '{ print $1 }'`

yes=`dd bs=4096 skip=$position count=256 if=$device | hexdump -C`

echo "In the next line you should see a pattern like:
00000000  79 0a 79 0a 79 0a 79 0a  79 0a 79 0a 79 0a 79 0a  |y.y.y.y.y.y.y.y.|
$yes
"

if [[ "`echo "$yes" | grep "y.y.y"`" == "" ]]; then
    echo "The pattern could not be checked. Something went wrong. Exiting."
    CLEAN;
else
    echo "Pattern confirmed."
fi

echo "Removing the temp file."
rm test-trim-by-desgua

echo "Syncing."
sync
sleep 1

if [[ "$fs" == "1" ]]; then
    echo "fstrim -v $pasta && sleep 2" ; echo
    fstrim -v $pasta
    sleep 2
fi

# Drop cache
echo 1 > /proc/sys/vm/drop_caches

echo "In the next line you should **NOT** see a yes pattern like:
00000000  79 0a 79 0a 79 0a 79 0a  79 0a 79 0a 79 0a 79 0a  |y.y.y.y.y.y.y.y.|
If you see, then trim is not working:
`dd bs=4096 skip=$position count=256 if=$device | hexdump -C`"

yes=`dd bs=4096 skip=$position count=256 if=$device | hexdump -C`
if [[ "`echo "$yes" | grep "y.y.y"`" != "" ]]; then
    echo "TRIM not working."
else
    echo "TRIM is working!"
fi
CLEAN;
}

if [[ "$method" == "1" ]]; then
    SDATEST;
    TEST;
elif [[ "$method" == "2" ]]; then
    LUKSTEST;
fi
exit 0
shareedit
edited Apr 13 '17 at 12:37

Community♦
1
answered Apr 29 '14 at 11:51

desgua
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