About the Master File Table zone reservation in Windows Vista and Windows Server 2008

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Source: Microsoft Support

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The NTFS File System contains a key file named the Master File Table (MFT) that stores information about the volume.  This core file contains an entry for every file on the volume and information about these files including size, time, date, permissions, etc.

 

For general information on the Master File Table, see:

http://msdn.microsoft.com/en-us/library/aa365230(VS.85).aspx

 

As more files are added to the NTFS volume, the MFT will grow to handle the larger files.  Very early versions of Windows would grow the MFT in small portions which would cause fragmentation.  Later versions of Windows introduced an MFT zone reservation.  This zone is a portion of the disk that is reserved for the MFT to grow into so that the MFT can remain continuous.  These previous versions of Windows use a percentage based algorithm to determine the zone size (default of 12.5%).  For information on earlier versions of Windows, see article:

 

174619  How NTFS reserves space for its Master File Table (MFT)

http://support.microsoft.com/default.aspx?scid=kb;EN-US;174619

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Windows Vista and Windows Server 2008 use a default size of 200MB for the initial MFT zone reservation.  As the MFT outgrows the default zone due to more files being added to the volume, the MFT will create another 200MB zone to grow into.  This change to fixed amount versus a percentage was done to deal with increasing size of volumes and create better efficiencies.

 

For example, in previous versions of Windows a 500GB NTFS volume would have a ~62GB MFT Zone Reservation (500MB x 12.5%).  So if the MFT only grew to the size of 100MB, the first 62GB of the volume would be “reserved” and data would not start until the end of the 62GB mark.

 

Starting with Windows Vista and Windows Server 2008, the MFT uses a fixed 200MB zone reservation so as not to reserve space that will never actually be used (note that the zone reservation can be used by data once the remainder of the volume is filled up - this is the same as in previous versions of Windows).

 

It is possible to adjust the size the MFT zone reservation uses.  If not changed, the default is set to 1.  The valid range is 1-4 where this is a multiplier of 200MB.  For example, if the data is set to 4, any newly create volumes initial MFT Zone Reservation will be 800MB and if it grows beyond this will grow in 800MB segments.  If this setting is created after a volume is created, the initial MFT zone reservation will be 200MB but future MFT zone reservations will be based on the multiplier.

 

There are two ways of making this change, a command-line utility and a registry change: Method 1

 

Use the included File System Utility (FSUtil) to change the MFT Zone Reservation from and elevated Command Prompt.  To do this, follow the below steps:

1.       Launch an elevated Command Prompt

2.       Type the following command

fsutil behavior set mftzone <n>

(Where <n> is between 1 and 4)

3.       Restart your computer Method 2

 

To use the registry to change the default MFT Zone Reservation size, perform the following steps:

 

1. Run Registry Editor (Regedt32.exe), and go to the following subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\FileSystem

2. From the Edit menu, click Add Value.

3. Type the following information in the dialog box:

Value Name: NtfsMftZoneReservation

Data Type : REG_DWORD

Data : (valid range is 1-4) 

4. Quit Registry Editor and restart your computer

 

For workstation or server profiles that have large MFT’s, it is possible that the MFT will be more “fragmented” however these fragments will be 200MB in size a piece so the performance impact will be negligible.  To determine how many fragments the MFT is in, run the following command under an elevated Command Prompt:

 

DEFRAG C: -A -V

                (Where C: is the volume you want to check)

 

In the output, review the section “Master File Table (MFT) fragmentation” and note the value of “Total MFT fragments”.  The defragmentation engine in Windows Vista and Windows Server 2008 can now consolidate the MFT.  For information on this, see the below article:

 

Features of the Windows Vista hard disk defragmentation utility

http://support.microsoft.com/kb/942092/en-us

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Article ID: 961095 - Last Review: December 11, 2008 - Revision: 1.0
APPLIES TO
  • Windows Server 2008 Datacenter
  • Windows Server 2008 Standard
  • Windows Server 2008 Enterprise
  • Windows Vista Enterprise 64-bit Edition
  • Windows Vista Home Basic 64-bit Edition
  • Windows Vista Ultimate 64-bit Edition
  • Windows Vista Business 64-bit Edition
  • Windows Vista Enterprise
  • Windows Vista Home Basic
  • Windows Vista Home Premium
  • Windows Vista Ultimate
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