File system fragmentation occurs when a file system does not store data on a disk in a sequential or contiguous manner. This increases the rate and time at which a hard disk must seek data and thus decreases throughput (the average rate data can be delivered or transmitted). Fragmentation is common on mechanical hard drives and they must be regularly defragmented. It is not an issue with solid state drives and defragmenting is actually discouraged because it shortens the life of the device.