It would be good to have a user interface for mapping FIDs to MDT/OST targets using the FID Location Database (FLDB). FLDB is available in memory on all clients, and in the fld.*.fldb file on the MDS. It might make sense to also add a fld.*.fldb file on the clients to facilitate this mapping (good for consistency with MDS, but problematic because it is not a "simple" file and would have to go into debugfs that is root only), or it could be an ioctl (easy to implement, but hard to run on the servers).