Fifth generation (5G) of mobile networks are expected to serve multiple heterogeneous use cases. These use cases are extremely diverse in terms of service requirements and bundling them in a single monolithic network is a challenge. Network slicing is identified as one of the main enablers of 5G systems, where multiple logical End-to-End (E2E) networks share the resources of a single physical network. Radio Resource Management (RRM) in a sliced network should be able to simultaneously fulfill the required services of slices, dynamically share the network and assure the independence of slices so that slices cannot affect each other negatively. In this paper, we study the existing mechanisms that provide similar features in legacy networks and demonstrate the contributions and shortcomings of such existing RRM mechanisms in a sliced network. Thereafter, we argue the need for a new entity that will complement the existing RRM mechanisms to be slice-aware. With the aid of system-level simulations, we compare different slicing schemes and illustrate the drawbacks of legacy networks in fulfilling the objectives of a fully sliced network. Moreover, we illustrate the capabilities of the slice-aware RRM in steering the network's Key Performance Indicators (KPIs). © 2019 IEEE.