You can access standard defrag on a computer by running the command "defrag" from the command prompt. Windows users can also access defrag from the Control Panel's System and Maintenance menu. You can also defrag using software like PerfectDisk.
VSS Defrag
VSS is a tool that creates point-in-time shadow copies or snapshots of files on the volume at predefined intervals. The snapshots can be used to recover files shortly after they are lost. VSS defrag is short for "Volume Shadow Copy Service defragmentation." VSS files can be defragmented by selecting to defragment only VSS files. VSS files can also be defragmented by selecting to defrag the system folders where shadow copies are stored.