Apparatus and method for managing namespaces in a Non-Volatile Memory Express (NVMe) controller environment. A non-volatile memory (NVM) is arranged to store map units (MUs) as addressable data blocks in one or more namespaces. A forward map has a sequence of map unit address (MUA) entries that correlate each of the MUs with the physical locations in the NVM. The MUA entries are grouped into immediately adjacent, contiguous ranges for each of the namespaces. A base MUA array identifies the address, within the forward map, of the beginning MUA entry for each namespace. A new namespace may be added by appending a new range of the MUA entries to the forward map immediate following the last MUA entry, and by adding a new entry to the base MUA array to identify the address, within the forward map, of the beginning MUA entry for the new namespace.