The key is encoded to point to a common container at the storage server.
This reduces the number of splits on the server side when load balancing.
Ingress to Azure storage can take advantage of earlier splits. We remove
the root path to the key and prefix a random GUID to the tail (or leaf
filename) of the key. Keys are thus broadly and randomly distributed over
a single container to ease load balancing on the storage server. When the
blob is committed it is renamed to its earlier key. Uncommitted blocks
are not cleaned up and we leave it to Azure storage to garbage collect
these
blocks.