core/src/main/java/org/sakaiproject/nakamura/api/lite/StorageClientUtils.java
public static String shardPath(String id) {
        String hash = insecureHash(id);
        return hash.substring(0, 2) + "/" + hash.substring(2, 4) + "/" + hash.substring(4, 6) + "/"
                + id;
    }
public static String shardPath(String id) {
        String hash = insecureHash(id);
        return hash.substring(0, 2) + "/" + hash.substring(2, 4) + "/" + hash.substring(4, 6) + "/"
                + id;
    }
For instance the SparsePrincipal uses it.