Linux · btrfs

How do you find out how much disk space a single btrfs subvolume or snapshot uses, and what's the difference between the rfer and excl columns?

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When you modify a file on btrfs, what happens to the original disk blocks holding that data?

A colleague assumes btrfs is the universally adopted next-gen Linux filesystem. Where does the vendor picture actually diverge?

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In btrfs terms, what is a subvolume, and how is it different from just making a directory?

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