A method and system writes data to a memory device including dynamic assignment of logical block addresses (LBAs) to physical write blocks. The method includes receiving a request to write data for a logical block address within an LBA range to the memory device. The method assigns the LBA range to a particular write block exclusively or non-exclusively, depending on the existence of previously assigned write blocks and the availability of unwritten blocks. A data structure may be utilized to record the recent usage of blocks for assigning non-exclusive write blocks. An intermediate storage area may be included that implements the dynamic assignment of LBA ranges to physical write blocks. Data in the intermediate storage area may be consolidated and written to the main storage area. Lower fragmentation and write amplification ratios may result by using this method and system.