swap: raw or file

"swap partition can yield better performance because the disk blocks are guaranteed to be contiguous. In the case of a swap file, however, the disk blocks may be scattered around the file system, which can be a serious performance hit in many cases. Many people use a swap file when they must add additional swap temporarily--for example, if the system is thrashing because of lack of physical RAM and swap. swap files are a good way to add swap on demand."

Running Linux, p.360