currently, only uncompressed tar can be writable?

[BingoKingo]

I tried, but renaming a file in tar is just duplicate a new one with new name after commit.
Can I put the renamed commit-overlay folder along with tar file by default without defining a new folder?

[mxmlnkn]

Unfortunately, you exactly pinpointed a todo in this feature:

ratarmount/ratarmount.py

Lines 1536 to 1538 in ea43572

	# TODO Support compressed archives by maybe using tarfile to read from the original and write to a temporary?
	# GNU tar does not support --delete on compressed archives unfortunately:
	# > This option does not operate on compressed archives.

And renaming is exactly one of the operations that is difficult. Other operations like modifying an existing file, could theoretically be implemented by simply appending the new file version and leaving the old file version in the TAR, even if that is not exactly space-saving.

Pull requests are welcome. Else, I might take another look in the coming months at using Python's tarfile module instead of GNU tar like the ToDo comment states.