1. A method, comprising: updating a first index node representing a file, the first index node comprising a plurality of entries representing extents of the file, wherein each entry of the plurality of entries comprises metadata that at least in part maps at least one logical address to at least one physical address of at least one data block of an extent of the file, wherein updating the first index node comprises at least one of adding, updating, or removing an entry at the first index node; determining whether a number of the plurality of entries included in the updated first index node exceeds a threshold corresponding to a number of extents; and responsive to determining that the number of the plurality of entries included in the updated first index node exceeds the threshold: generating a copy-on-write (COW) B-tree data structure containing the plurality of entries representing the extents of the file; and modifying the first index node to replace the plurality of entries representing the extents of the file with a new entry that points to the COW B-tree data structure.