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I have set up LVM to cache a logical volume (located on an HDD) on a partition of an SSD (in writeback mode if this matters). As far as I can tell, this works correctly and the cache uses all available space.

Now, I am wondering whether this setup issues TRIM command to the SSD and whether issuing such commands is necessary (or reasonable) to extend the SSD's lifetime. I have added discard to the options in /etc/fstab for the cached logical volume's entry. However, I have no idea how this affects the cache partition nor do I have an idea on how to test whether TRIM commands are issued.

  • Why do you suspect trim is being issued? – Nils Sep 20 '18 at 17:00
  • @Nils The problem is rather that I suspect no TRIM commands are issued and that this might negatively affect the SSD's lifetime. – JPW Sep 23 '18 at 11:58
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To test it, simply use:

fstrim -v -a

This will trim all your SSD block devices (including cached volumes) and print out how much has been trimmed.

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