dd can copy block by block from one block device to another ddrescue can do the same, but will handle errors better e2image understands ext2/3/4 filesystems a

dd can copy block by block from one block device to another ddrescue can do the same, but will handle errors better e2image understands ext2/3/4 filesystems and can copy only the blocks in use, which can really help (though don't know how it works if it encounters an error)