How does the filesystem (ext4) store TRIM information?

If you have the discard mount option, it will block every time you delete a file, and thus file deletion will take far longer. So that is ...

It will slow down your drive as TRIM is applied constantly. A better option would be to use `fstrim` periodically -- I use it with a systemd timer.

You can perform online block discard operations to automatically discard unused blocks on all supported file systems.

These kernels support realtime discard for ext4 and xfs. To use the kernel realtime discard feature, you must mount with the mount -o discard ... Terminology · Current status · Kernel support · Userland support

I tried to turn off TRIM (discard) on my ext4 filesystem, but I did not succeed. I tried to add nodiscard option into /etc/fstab , but I can still see this.

As of 2.6.37, it should be present (source). The kernel doesn't do it in the background, the block discard process is currently designed to be run on demand.

Attempting to run fstrim on my root partition (which is ext4 on a LVM logical volume, single physical volume—an SSD supporting TRIM) produces an ...

Once you reboot or re-mount the filesystem, it just TRIMs empty space all over again. So this could be an in-memory structure that isn't stored ...

I have discard enabled, but yet fstrim -v tells me it had trimmed some amount of data, which seems to be proportional to the amount of files deleted.

According to ext4(5), ext4 supports discard, but not the async variant. That's a btrfs feature. Weekly fstrims are good enough though, don't ...