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Is it safe to run fstrim -v / if I have rotational HDD mounted in /dev/media?

For now, whenever I want to trim the SSD I just unmount those drives, run fstrim and mount them again.

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up vote 2 down vote accepted

The root directory "/" in your fstrim command is a mount point, not a path. As such, trim applies only to that mounted partition and will not recurse through the path into a new mountpoint.

You can double check this action by running manually with the verbose flag on (-v, and I see it there in your command). If there are no errors, you're fine.

This point about the mountpoint is implied, but not explicit in the man page: and on archlinux: but I also found other forum posts with the same assertion.

p.s. I found the archlinux page quite informative, laying out various ways to achieve SSD performance improvements. One noteworthy detail I saw there, when discussing the "discard" method was that the discard flag was added to each mount point separately in their example, even though one partition was mounted downstream of the other (/ and /home). Good luck!

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