Usually just specifying a reasonable blocksize works for me. bs=1m or so. Without that it does literally take hours. I suspect the default blocksize is really

Usually just specifying a reasonable blocksize works for me. bs=1m or so. Without that it does literally take hours. I suspect the default blocksize is really small (1?) and combined with uncached/unbuffered writes to slower devices, it just kills all performance outright. Edit: answered! https://news.ycombinator.com/item?id=13350002 https://news.ycombinator.com/item?id=13350002