Checking if SSD trim is working (discard)

Note that if your kernel is before 2.6.33 you can check, but it won’t be working !

in the case that you don’t want to update your kernel, and you just want to trim your disk, try wiper.sh or fstrim, both are command line tools that you can run manually or put in a cron job. if you do want to update your kernel, here is how on debian squeeze

So for example, if you are on debian 6 squeeze, you need to get a kernel from the backports (add the line “deb http://backports.debian.org/debian-backports squeeze-backports main” to your /etc/apt/sources.list then apt-get update then apt-get -t squeeze-backports install linux-image-3.2.0-0.bpo.2-amd64) to get the new kernel, it will then work.

I assume you already have an ext4 file system with discard option in fstab as described on this website

Also note: Many modern SSDs will not reclaim the TRIMmed space., so if using the test below you see zeros, discard (trim) is working 100%, if you don’t. it may or may not be working… but if you wait fdor a significant amount of time, then reboot, the zeros should appear in that exact location even if the disk does not reclaim instantly … happyt trimming, now to the procedure

now, write a file to the ssd (random numbers)
dd if=/dev/urandom of=/hds/ssd300/myfile.bin bs=1M count=3

Find the location where the file begins
hdparm –fibmap /hds/ssd300/myfile.bin

Now, take note of the start address and use it in this command replacing xxxxx

hdparm –read-sector xxxxxx /dev/sdb
You should see random numbers

Delete the file
rm /hds/ssd300/myfile.bin
Sync with the command
sync

Wait for 2 minutes
the issue the same command to read again
hdparm –read-sector xxxxxx /dev/sdb
You should now see all zeros, if you do not, the disk has not been trimmed 🙂

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