How would fstrim.timer work when both SDD & HDD exist?

Will HDD also be trimmed while it is not necessary?

TRIM doesnt work on the HDD … enabling the timer will just mean your SSD runs fstrim from time to time.


According to the post below, HDD is also trimmed.

Fstrim only works with SSDs.


If you open

man fstrim

and read the documentation you will find that fstrim only tries to discard for devices that supports it.


       -a, --all
           Trim all mounted filesystems on devices that support the
           discard operation.

Which essentially means that devices which do not support it are skipped.

For your reference to an almost 3 year old topic - I’d say - either fstrim got smarter or the poster had other issues.

Please heed the warning in the manual

       Running fstrim frequently, or even using mount -o discard,
       might negatively affect the lifetime of poor-quality SSD
       devices. For most desktop and server systems a sufficient
       trimming frequency is once a week. Note that not all devices
       support a queued trim, so each trim command incurs a
       performance penalty on whatever else might be trying to use
       the disk at the time.


Another thing to note is

If you do not enable the fstrim.timer - then after some time - depending on your usage - e.g. a lot of ISO files coming and going and the size of your SSD - you will run into mysterious slow-down of your disk - this is the consequence of not running trim - because trim free’s up memory cell marked as in use even the content has been deleted.

This is normal and part of the design - a design that makes it very hard to scrub a SSD device completely for reuse. It this is a topic that interest you the following links are interesting and very educating

This research paper is an interesting read.


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