This paper presents a novel offline buffer management scheme for flash-based storage and memory sys-tems. NAND flash memory is a promising storage technology to accelerate IO performance which has been deployed widely in the high-performance data storage systems. The widespread use of this technology unleashed new products which employ flash memory in write intensive applications like server-side caches and in-memory database systems. However, due to limited endurance and relatively high write latency, it is critical to minimize writes to the flash memory in these use cases. Therefore, a small write buffer is used on the top of flash memory to coalesce write requests and reduce write amplification. Although multiple schemes have been proposed to enhance write buffer functionality, still it is not clear how much further these schemes can reduce write amplification and mitigate flash limitations. In this paper, we have focused on this issue and proposed a novel Offline Write Buffer Policy (OWBP) which can reduce flash write amplification by making policy decisions based on futurewrite requests information. This scheme can provide a lower bound for the erase count while maintaining a competitive ratio of buffer hit. We believe OWBP is a useful addition to the flash memory firmware developer community for the evaluation of practical (online) write-buffer management schemes.