It’s interesting, however, if you mkfs.ext4 without -E ssd, or through some weirdness in your driver chain the filsystem doesn’t know it can discard, then everything everywhere sucks for everyone, a cow fs is worse because no blocks are ever overwritten till the end, and the block map becomes a disaster while performance goes down the drain.
Nowadays this rarely happens outside of very broken USB mass storage chips.
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The fs does cow then releases the old block if appropriate.
The ssd has a tracking map for all blocks, it’s cow relies on a block being overwritten to free the old block.
Basically it works out the same either way.
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It’s interesting, however, if you mkfs.ext4 without -E ssd, or through some weirdness in your driver chain the filsystem doesn’t know it can discard, then everything everywhere sucks for everyone, a cow fs is worse because no blocks are ever overwritten till the end, and the block map becomes a disaster while performance goes down the drain.
Nowadays this rarely happens outside of very broken USB mass storage chips.
This is why we used to have the fstrim command.