It's a very similar idea. Traditional Unix-ish filesystems, with inodes and indirect nodes are a lot like b-trees, but ones where the indices are block numbers

It's a very similar idea. Traditional Unix-ish filesystems, with inodes and indirect nodes are a lot like b-trees, but ones where the indices are block numbers and where you can only append indices, trim, or replace indices. The ZIL (ZFS intent log) is a mechanism for amortizing the write magnification of copy on write trees.