Lustre File Identifiers
~~~~~~~~~~~~~~~~~~~~~~~
[[fids]]

----
struct lu_fid {
	__u64 f_seq;
	__u32 f_oid;
	__u32 f_ver;
};
----

File IDs ('fids') are 128-bit numbers that uniquely identify files and
directories on the MDTs and OSTs of a Lustre file system. The fid for
a Lustre file or directory is the fid from the corresponding MDT entry
for the file. Each of the data objects for that file will also have a
fid for each corresponding piece of the file on each of the
OSTs. Encoded in the fid is the target on which that file metadata or
file fragment resides. The map from fid to target is in the File
Location DataBase (FLDB).