DEFRAG.exe – Windows CMD Command

Defragment hard drive volumes.

Syntax
      Perform analysis only:
      DEFRAGs /A  vol_to_defrag [Options]

      Defragment (default operation)
      DEFRAG [/D] vol_to_defrag [Options]

      Perform the proper optimization for each media type:
      DEFRAG /O vol_to_defrag [Options]

      Perform free space consolidation:
      DEFRAG /X vol_to_defrag [Options]

      Track an operation already in progress on a volume:
      DEFRAG /T volume

vol_to_defrag:

    This can be any of:

    volume  The drive letter or mount point path of the volume(s) to be defragmented or analyzed.
            To specify multiple volumes separate the names with spaces.
    /C      Perform the operation on all volumes.
    /E volume_name(s)   Perform the operation on all volumes Except those specified.

Options:
    /G      Optimize the storage tiers on the specified volumes.
    /H      Run the operation at normal priority (default is low).
    /I n    Run Tier optimization 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.
    /U      Print the progress of the operation on the screen.
    /V      Print verbose output containing the fragmentation statistics

Defrag has an undocumented option/b (boot optimization) which will clear out the Windows\Prefetch directory. Deleting prefetch files will make the machine boot more slowly so this is not recommended.

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.

Supported file systems: NTFS, ReFS, Fat or Fat32.

To run Defrag, you must be a member of the Administrators group on the local computer or have been delegated the appropriate authority. When working defrag will display a blinking cursor.

On a tiered volume traditional defrag (/D) is performed only on the Capacity tier. (See FSUTIL tiering)

Some file system volumes or drives cannot be defragmented:

• Volumes that the file system has locked.
• Volumes that the file system has marked as dirty, which indicates possible corruption. Run CHKDSK on a dirty volume to resolve this.
  Use the fsutil dirty query command to determine if a volume is dirty.

Volume names can be given either using the assigned drive letter (C:\) or the full volume name/path (\\?\Volume{…)

To obtain a list of volume_names using PowerShell:

PS C:\> Get-CimInstance Win32_Volume | Format-Table Name, Label, FreeSpace, Capacity

Free space consolidation (/X) takes all free sectors on the volume and arranges them together so they are contiguous. This is normally done only when you intend to re-size the volume with DISKPART SHRINK to make it smaller.
Ensure you have a good backup before running any consolidate/shrink process as this has a tendency to fail.

Defrag’s scheduled task runs as a maintenance task and by default is scheduled to run every 7 days at 2 am. An Administrator can change the frequency using the Optimize Drives application.

Examples:

Analyse drive C: to see if it needs to be defragmented:

DEFRAG /A C:

Defragment drive c with verbose output saved to a file:

DEFRAG c: /U /V > FileName.txt

Defragment two drives in parrallel:

DEFRAG C: D: /M