How does Windows calculate the fragmentation percentage?

3

When running defrag -a -v C: on Windows 2008 R2, I got the following output:

Windows Disk Defragmenter
Copyright (c) 2006 Microsoft Corp.

Analysis report for volume C:

    Volume size                         = 40.00 GB
    Cluster size                        = 4 KB
    Used space                          = 13.94 GB
    Free space                          = 26.06 GB
    Percent free space                  = 65 %

File fragmentation
    Percent file fragmentation          = 19 %
    Total movable files                 = 73,181
    Average file size                   = 233 KB
    Total fragmented files              = 1,574
    Total excess fragments              = 5,611
    Average fragments per file          = 1.09
    Total unmovable files               = 21

The Percent file fragmentation value seems very strange to me. From the file counts, 1574 fragmented files is only 2% of the total number of files.

How does Windows calculate the Percent file fragmentation value?

jpa

Posted 2015-03-05T15:59:46.333

Reputation: 201

19% is the amount of fragmentation across all files compared to the total amount of file segments across each sector. – Ramhound – 2015-03-05T16:26:05.003

Windows skips files over 64MB, so I guess the 19% are calculated from the files smaller 64MB: "In Windows XP, any file that is split into more than one piece is considered fragmented. Not so in Windows Vista if the fragments are large enough – the defragmentation algorithm was changed (from Windows XP) to ignore pieces of a file that are larger than 64MB. As a result, defrag in XP and defrag in Vista will report different amounts of fragmentation on a volume." http://blogs.msdn.com/b/e7/archive/2009/01/25/disk-defragmentation-background-and-engineering-the-windows-7-improvements.aspx

– magicandre1981 – 2015-03-05T18:18:16.863

@magicandre1981 Note that only 14 GB of space is in use. That means that there can't be more than 200 files of over 64MB. So I don't think that can explain the difference, when total number of files is 73 181. – jpa – 2015-03-06T06:15:15.130

Answers

1

It seems that:

Percent file fragmentation = Percent free space (after defragmentation) - Percent free space (before defragmentation)

In other words, the percent free space added by performing full defragmentation.

As you can see, 7 % = 31 % - 24 %:

C:\Windows\system32>defrag c: -w -v
Windows Disk Defragmenter
Copyright (c) 2006 Microsoft Corp.`

Defragmentation report for volume C:

    Volume size                         = 74.53 GB
    Cluster size                        = 4 KB
    Used space                          = 55.96 GB
    Free space                          = 18.57 GB
    Percent free space                  = 24 %

File fragmentation
    Percent file fragmentation          = 7 %
    Total movable files                 = 203,178
    Average file size                   = 342 KB
    Total fragmented files              = 3,641
    Total excess fragments              = 32,280
    Average fragments per file          = 1.19
    Total unmovable files               = 26

Free space fragmentation
    Free space                          = 18.57 GB
    Total free space extent             = 22,689
    Average free space per extent       = 858 KB
    Largest free space extent           = 4.09 GB

Folder fragmentation
    Total folders                       = 40,150
    Fragmented folders                  = 155
    Excess folder fragments             = 567

Master File Table (MFT) fragmentation
    Total MFT size                      = 203 MB
    MFT record count                    = 205,234
    Percent MFT in use                  = 98
    Total MFT fragments                 = 3

    Note: On NTFS volumes, file fragments larger than 64MB are not included in the fragmentation statistics

Defragmentation report for volume C:

    Volume size                         = 74.53 GB
    Cluster size                        = 4 KB
    Used space                          = 50.90 GB
    Free space                          = 23.62 GB
    Percent free space                  = 31 %

File fragmentation
    Percent file fragmentation          = 0 %
    Total movable files                 = 203,178
    Average file size                   = 342 KB
    Total fragmented files              = 3
    Total excess fragments              = 1,152
    Average fragments per file          = 1.00
    Total unmovable files               = 26

Free space fragmentation
    Free space                          = 23.62 GB
    Total free space extent             = 10,109
    Average free space per extent       = 2 MB
    Largest free space extent           = 6.99 GB

Folder fragmentation
    Total folders                       = 40,150
    Fragmented folders                  = 1
    Excess folder fragments             = 0

Master File Table (MFT) fragmentation
    Total MFT size                      = 203 MB
    MFT record count                    = 205,234
    Percent MFT in use                  = 98
    Total MFT fragments                 = 3

    Note: On NTFS volumes, file fragments larger than 64MB are not included in the fragmentation statistics

C:\Windows\system32>

On the other hand, when, after defragmenting a drive, the Percent free space does not change, nor the Percent file fragmentation does not change, even if the Total fragmented files number does change: 

C:\Windows\system32>defrag d: -w -v -f
Windows Disk Defragmenter
Copyright (c) 2006 Microsoft Corp.

Defragmentation report for volume D:

    Volume size                         = 932 GB
    Cluster size                        = 4 KB
    Used space                          = 841 GB
    Free space                          = 90.89 GB
    Percent free space                  = 9 %

File fragmentation
    Percent file fragmentation          = 2 %
    Total movable files                 = 400,108
    Average file size                   = 2 MB
    Total fragmented files              = 7,671
    Total excess fragments              = 1,420,753
    Average fragments per file          = 4.70
    Total unmovable files               = 7

Free space fragmentation
    Free space                          = 90.89 GB
    Total free space extent             = 213,633
    Average free space per extent       = 446 KB
    Largest free space extent           = 27.46 GB

Folder fragmentation
    Total folders                       = 16,189
    Fragmented folders                  = 526
    Excess folder fragments             = 2,304

Master File Table (MFT) fragmentation
    Total MFT size                      = 421 MB
    MFT record count                    = 405,678
    Percent MFT in use                  = 94
    Total MFT fragments                 = 3

    Note: On NTFS volumes, file fragments larger than 64MB are not included in the fragmentation statistics

Defragmentation report for volume D:

    Volume size                         = 932 GB
    Cluster size                        = 4 KB
    Used space                          = 841 GB
    Free space                          = 90.89 GB
    Percent free space                  = 9 %

File fragmentation
    Percent file fragmentation          = 2 %
    Total movable files                 = 400,108
    Average file size                   = 2 MB
    Total fragmented files              = 353
    Total excess fragments              = 1,226,342
    Average fragments per file          = 4.19
    Total unmovable files               = 7

Free space fragmentation
    Free space                          = 90.89 GB
    Total free space extent             = 260,094
    Average free space per extent       = 366 KB
    Largest free space extent           = 27.46 GB

Folder fragmentation
    Total folders                       = 16,189
    Fragmented folders                  = 1
    Excess folder fragments             = 0

Master File Table (MFT) fragmentation
    Total MFT size                      = 421 MB
    MFT record count                    = 405,678
    Percent MFT in use                  = 94
    Total MFT fragments                 = 3

    Note: On NTFS volumes, file fragments larger than 64MB are not included in the fragmentation statistics

C:\Windows\system32>

misterr

Posted 2015-03-05T15:59:46.333

Reputation: 11

1

This calculation is hidden, the information is delivered by Win32_DefragAnalysis class:

The Win32_DefragAnalysis class represents fragmentation values on a volume. An instance of the Win32_DefragAnalysis class is passed as an out parameter from the Win32_Volume methods DefragAnalysis and Defrag.

class Win32_DefragAnalysis
{
  uint64 AverageFileSize;
  real64 AverageFragmentsPerFile;
  real64 AverageFreeSpacePerExtent;
  uint64 ClusterSize;
  uint64 ExcessFolderFragments;
  uint32 FilePercentFragmentation;
  uint64 FragmentedFolders;
  uint64 FreeSpace;
  uint32 FreeSpacePercent;
  uint32 FreeSpacePercentFragmentation;
  uint64 LargestFreeSpaceExtent;
  uint32 MFTPercentInUse;
  uint64 MFTRecordCount;
  uint64 PageFileSize;
  uint64 TotalExcessFragments;
  uint64 TotalFiles;
  uint64 TotalFolders;
  uint64 TotalFragmentedFiles;
  uint64 TotalFreeSpaceExtents;
  uint64 TotalMFTFragments;
  uint64 TotalPageFileFragments;
  uint32 TotalPercentFragmentation;
  uint64 TotalUnmoveableFiles;
  uint64 UsedSpace;
  string VolumeName;
  uint64 VolumeSize;
};

duDE

Posted 2015-03-05T15:59:46.333

Reputation: 14 097

this class is not port of any client OS. – magicandre1981 – 2015-03-05T18:15:16.720

Doesn't really answer the question. I would expect the FilePercentFragmentation member to be documented somewhere, but cannot find anything. – jpa – 2015-03-06T06:18:37.950

Asked: 2015-03-05T15:59:46.333

Viewed: 2 146 times

Active: 2016-01-02T16:33:04.870