DEFRAG.exe – Windows CMD Command
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Defragment hard drive volumes.
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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.
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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 |
