Apparatus and method for managing shared resources in a data storage device such as a solid-state drive (SSD). In some embodiments, a non-volatile memory (NVM) has a population of semiconductor memory dies which are divided into die sets for different users. Each die set includes user garbage collection units (GCUs) for storage of user data blocks by the associated user and overprovisioned global GCUs to store user data blocks from the users of the other die sets. When an imbalance condition exists such that the workload traffic level of a first die set exceeds a workload traffic level of a second die set, at least one host I/O command for the first die set is offloaded for servicing using a selected global GCU of the second die set. The offloaded data may be subsequently transferred to the first die set after the imbalance condition is resolved.