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Reading through a Disk Defragmenter analysis report I noticed that my NTFS Master File Table was 6.87GB in size, but only 4% of it was reported as in use.

Is this something that could cause NTFS performance issues? Is there anything that can be done about it?

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up vote 5 down vote accepted

NTFS reserves 12.5% of the volume (it sounds like this is roughly a 54GB volume) for the MFT when the volume is formatted (unless you override this behaviour). This prevents MFT fragmentation. At 4% usage of your MFT, it sounds like you're not in any danger of causing NTFS to allocate additional space for the MFT.

If the space allocated for the MFT is used up, NTFS will allocate additional space for the MFT. The "Disk Defragmenter" functionality in Windows XP and Windws Server 2003 (presumably also in newer versions of Windows) can defragment the MFT, so the spectre of MFT fragmentation that was a bigger deal in the NT 4.0 time-frame isn't such a big deal today.

Basically, you've got nothing to worry about.

See for background from Microsoft.

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+1 - won't cause "performance issues" unless it gets large enough to start having fragmentation itself... – TheCleaner Oct 5 '09 at 16:10

The MFT will fragment only if it is unable to expand contiguously. This can occur if the free space on the volume drops to less than ~ 85%, and/or if there is a large number of small files on the volume (Very small files ~1kB are stored in the MFT itself).

The capability for defragging the MFT is built into XP and higher versions, but in XP atleast, the default defragger actually does not utilize this feature, instead a third party utility such as Diskeeper is required. Most of the MFT can be defragged by Diskeeper without requiring a boot-time defrag (unlike previously), and a boot-time defrag will fix the remainder.

Anyway, with only 4% of the MFT in use, there is absolutely nothing to worry about at the moment :)

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