Swap space is a method by which an operating system can move information out of memory and store it elsewhere until it is needed again. Swap space can generally be thought of an extension of the computer's memory which lives on the hard drive. In the past, having swap space was important as computers had relatively little memory and could quickly run out of available RAM. Unused data could be punted to swap while more urgent tasks were handled in memory. These days though computers tend to have a lot of memory and it raises the question of whether there is any point in having swap space anymore and, if so, how much? The Red Hat team has explored this topic in a post called Do we really need swap on modern systems? "In the past, some application vendors recommended swap of a size equal to the RAM, or even twice the RAM. Now let us imagine the above-mentioned system with 2GB of RAM and 2GB of swap. A database on the system was by mistake configured for a system with 5GB of RAM. Once the physical memory is used up, swap gets used. As the swap disk is much slower than RAM, the performance goes down, and thrashing occurs. At this point, even logins into the system might become impossible. As more and more memory gets written to, eventually both physical and swap memory are completely exhausted and the OOM killer kicks in, killing one or more processes. In our case, quite a lot of swap is available, so the time of poor performance is long. Now, let us imagine the above situation with no swap configured. As the system runs out of RAM, it has no swap to hand out. There is almost no time frame of reduced performance - the OOM kicks in immediately." The article goes on to talk about issues to consider when deciding whether to use swap space.