The article describes a third way which is neither mtime nor hashes. It's basically a database of (mtime, size, inode number, file mode, owner, group) tuples.

The article describes a third way which is neither mtime nor hashes. It's basically a database of (mtime, size, inode number, file mode, owner, group) tuples. So it still requires keeping a database. But because all of that would come out of inodes, it avoids all the I/O of reading the files' contents. Compared to mtime, it's harder to implement, but more resilient and at a similar cost. Compared to hashes, it's almost as resilient but much faster.