Provided are a computer program product, system and method for managing read/write operations in a hybrid memory device system. Determinations are made of an available physical address in a first memory device for a data block to allocate for metadata for a file or directory in a file system and a first logical address corresponding to the available physical address in a first range of logical addresses. Determinations are made of an available physical address in a second memory device for a data block to allocate for the file or directory in the file system and a second logical address corresponding to the available physical address in the second memory device in a second range of logical addresses. The second logical address is used to access the data block allocated to the file or directory in the file system.