The benefit of using InodeID to uniquely identify a file can be multiple folds. Here are a few of them:
1. uniquely identify a file cross rename, related JIRAs include
2. modification checks in tools like distcp. Since a file could have been replaced or renamed to, the file name and size combination is no t reliable, but the combination of file id and size is unique.
3. id based protocol support (e.g., NFS)
4. to make the pluggable block placement policy use fileid instead of filename (