directory does not yet exist in the target, it is marked "New Dir"; if the directory is empty and the /E option is not used, or it contains no files meeting the criteria, a new directory will not be created. If the /NFL (no file names in log) option is not used, the files being copied will be listed after the name of the directory they are in. At the end of the output is a table giving numbers of directories, files, and bytes. For each of these, the table gives the total number found in the source, the number copied (including directories marked "New Dir" even if they are not copied), the number skipped (because they already exist in the target), and the number of mismatches, FAILED, and extras. "Failed" can mean that there was an I/O error that prevented a file being copied, or that access was denied. There is also a row of time taken (in which the time spent on failed files seems to be in the wrong column). Bandwidth throttling Robocopy's "inter-packet gap" (IPG) option allows some control over the network bandwidth used in a session. In theory, the following formula expresses the delay (, in milliseconds) required to simulate a desired bandwidth (BD, in kilobits per second), over a network link with an available bandwidth of BA kbps: In practice however, some experimentation is usually required to find a suitable delay, due to factors such as the nature and volume of other traffic on the network. The methodology employed by the IPG option may not offer the same level of control provided by some other bandwidth throttling technologies, such as BITS (which is used by Windows Update and BranchCache). Limitations Robocopy does not copy open files. Any process may open files for exclusive read access by withholding the FILE_SHARE_READ flag during opening. Even Robocopy's Backup mode will not touch those files. (Backup mode instead runs Robocopy as a "Backup Operator". This allows Robocopy to override permissions settings, specifically, NTFS ACLs). Normally Volume Shadow Copy Service is used for such situations, but Robocopy does not use it. Consequently, Robocopy is not suitable for backing up live operating system volumes. However, a separate utility such as 'ShadowSpawn' (Free, Open Sourced, and MIT Licensed) or 'GSCopyPro' () or (included with Windows Server 2008), can be used beforehand to create a shadow copy of a given volume, which