From Nginx official site there are two method to store remote upstream on local file system, "proxy_cache" and "proxy_store", the document describes clearly on how to configure, but still I have problem on the differences. Months ago I did some test over the both and found proxy_cache owns far better performance, and I thought proxy_cache is "cache in memory", recently after diving into source code, I recognized both are file based, so i'm not sure if it could afford high connection where disk probably becomes the bottleneck.