Packet replay is an important way to reproduce real traffic for network test. Many works focus on the performance and accuracy of packet generation based on hardware, such as NP and FPGA, in order to replace inefficient software based packet replay tools. However, limited onboard storage space constrains the size of trace file. In this paper, we design a novel FPGA based packet replay tool called iTester which supports to replay large trace file without impairing the performance and accuracy. It combines high-performance feature of FPGA with vast storage space in host PC. In RAM disk mode, file of Giga Bytes, depending on the memory size in host PC, can be replayed at 10Gbps while the average error of packet gap is kept within 10ns. Additionally, compared to copy with packet, it has a 69% performance improvement in RAM disk mode by adjusting the block size for memory copy.