Windows command line defrag command

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Applies to: Windows 10, Windows Server (Semi-Annual Channel), Windows Server 2016, Windows Server 2012 R2, Windows Server 2012

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Locates and consolidates fragmented files on local volumes to improve system performance.

Membership in the local Administrators group, or equivalent, is the minimum required to run this command. While defrag is analyzing and defragmenting a volume, it displays a blinking cursor. When defrag is finished analyzing and defragmenting the volume, it displays the analysis report, the defragmentation report, or both reports, and then exits to the command prompt.


defrag <volumes> | /c | /e <volumes>    [/h] [/m [n]| [/u] [v]]
defrag <volumes> | /c | /e <volumes> /a [/h] [/m [n]| [/u] [v]]
defrag <volumes> | /c | /e <volumes> /x [/h] [/m [n]| [/u] [v]]
defrag <volume> [<parameters>]


Parameter Description
<volume> Specifies the drive letter or mount point path of the volume to be defragmented or analyzed.
/a Perform analysis on the specified volumes.
/c Perform the operation on all volumes.
/d Perform traditional defrag (this is the default). On a tiered volume though, traditional defrag is performed only on the Capacity tier.
/e Perform the operation on all volumes except those specified.
/g Optimize the storage tiers on the specified volumes.
/h Run the operation at normal priority (default is low).
/i [n] Tier optimization would run for at most n seconds on each volume.
/k Perform slab consolidation on the specified volumes.
/l Perform retrim on the specified volumes.
/m [n] Run the operation on each volume in parallel in the background. At most n threads optimize the storage tiers in parallel.
/o Perform the proper optimization for each media type.
/t Track an operation already in progress on the specified volume.
/u Print the progress of the operation on the screen.
/v Print verbose output containing the fragmentation statistics.
/x Perform free space consolidation on the specified volumes.
/? Displays this help information.


  • You can’t defragment specific file system volumes or drives, including:
    • Volumes locked by the file system.
    • Volumes the file system marked as dirty, indicating possible corruption.
      You must run chkdsk before you can defragment this volume or drive. You can determine if a volume is dirty by using the fsutil dirty command.
    • Network drives.
    • CD-ROMs.
    • File system volumes that aren’t NTFSReFSFat or Fat32.
  • To perform this procedure, you must be a member of the Administrators group on the local computer, or you must have been delegated the appropriate authority. If the computer is joined to a domain, members of the Domain Admins group might be able to perform this procedure. As a security best practice, consider using Run As to perform this procedure.
  • A volume must have at least 15% free space for defrag to completely and adequately defragment it. defrag uses this space as a sorting area for file fragments. If a volume has less than 15% free space, defrag will only partially defragment it. To increase the free space on a volume, delete unneeded files or move them to another disk.
  • While defrag is analyzing and defragmenting a volume, it displays a blinking cursor. When defrag is finished analyzing and defragmenting the volume, it displays the analysis report, the defragmentation report, or both reports, and then exits to the command prompt.
  • By default, defrag displays a summary of both the analysis and defragmentation reports if you do not specify the /a or /v parameters.
  • You can send the reports to a text file by typing >FileName.txt, where FileName.txt is a file name you specify. For example: defrag volume /v > FileName.txt
  • To interrupt the defragmentation process, at the command line, press CTRL+C.
  • Running the defrag command and Disk defragmenter are mutually exclusive. If you are using Disk defragmenter to defragment a volume and you run the defrag command at a command-line, the defrag command fails. Conversely, if you run the defrag command and open Disk defragmenter, the defragmentation options in Disk defragmenter are unavailable.


To defragment the volume on drive C while providing progress and verbose output, type:

defrag c: /u /v

To defragment the volumes on drives C and D in parallel in the background, type:

defrag c: d: /m

To perform a fragmentation analysis of a volume mounted on drive C and provide progress, type:

defrag c: mountpoint /a /u

To defragment all volumes with normal priority and provide verbose output, type:

defrag /c /h /v

Scheduled task

The defragmentation process runs scheduled task as a maintenance task, which typically runs every week. As an Administrator, you can change the how often the task runs by using the Optimize Drives app.

  • When run from the scheduled task, defrag uses the below policy guidelines for SSDs:
    • Traditional optimization processes. Includes traditional defragmentation, for example moving files to make them reasonably contiguous and retrim. This is done once per month. However, if both traditional defragmentation and retrim are skipped, then analysis isn’t run. Changing the frequency of the scheduled task does not affect the once per month cadence for the SSDs.
    • If you manually run traditional defragmentation on a SSD, between your normally scheduled runs, the next scheduled task run performs analysis and retrim, but skips traditional defragmentation on that SSD.
    • If you skip analysis, you won’t see an updated Last run time in the Optimize Drives app. Because of that, the Last run time can be up to a month old.
    • You might find that scheduled task hasn’t defragmented all volumes. This is typically because:
      • The process won’t wake the computer to run.
      • The computer isn’t plugged in. The process won’t run if the computer is running on battery power.
      • The computer started back up (resumed from idle).