Generating large-scale holograms using computer-generated holography (CGH) requires vast memory resources, often exceeding available system memory. While out-of-core processing offers a solution, it introduces significant I/O bottlenecks during diffraction, a core operation in CGH. To address this challenge, we present the COMBO system, a novel out-of-core processing framework designed to accelerate large-scale diffraction computation. COMBO integrates block-wise data handling with GPU-accelerated compression to significantly enhance I/O efficiency, further optimized through the use of multiple SSDs. Experimental results show that COMBO achieves up to 4.16 times faster performance compared to prior out-of-core methods while maintaining high-quality holographic reconstructions. Additionally, we successfully generated a 256K hologram, requiring tera-scale computational space (e.g., 4TB), on a system with only 64GB of system memory.