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I recently became aware of MFT Zone, which is one of four levels: 1, 2, 3, 4. An NTFS volume is formatted with default Level 1, or 12.5% according to Microsoft (unless user specifies different level). Each level is a mulitplier of 200MB after the initial NTFS formatting of a drive. So, if I use level 2, MFT Zone size increases in 2(200MB) chunks = 400MB. Level 3 increases in 3(200MB) = 600MB chunks. Upon initial format, 12.5% * (disk size) = MFT Zone size because default is level 1.

You can change the size of the MFT zone for newly created volumes by to correspond to a percentage of the volume to be used as the MFT zone. The MFT zone sizes follow: • Setting 1, the default, reserves approximately 12.5 percent of the volume.

• Setting 2 reserves approximately 25 percent.

• Setting 3 reserves approximately 37.5 percent.

• Setting 4 reserves approximately 50 percent.

https://technet.microsoft.com/en-us/library/cc781134(v=ws.10).aspx

So, why would a drive have an MFT Zone size less than 12.5%?

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2 Answers 2

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While it says 12.5% here:

Because of the importance of the MFT to NTFS and the possible impact on performance if this file becomes highly fragmented, NTFS makes a special effort to keep this file contiguous. NTFS reserves 12.5 percent of the volume for exclusive use of the MFT until and unless the remainder of the volume is completely used up. Thus, space for files and directories is not allocated from this MFT zone until all other space is allocated first.

it does later say this:

A new registry parameter was introduced in Service Pack 4 for Windows NT 4.0 that can increase the percentage of a volume that NTFS reserves for its master file table. NtfsMftZoneReservation is a REG_DWORD value that can take on a value between 1 and 4, where 1 corresponds to the minimum MFT zone size and 4 corresponds to the maximum. If the parameter is not specified or an invalid value is supplied, NTFS uses a default value of 1 for this parameter. The exact ratios that correspond to each setting are undocumented because they are not standardized and may change in future releases. In order to know what setting is best for your environment, it may be necessary to experiment with different values.

There is also this line in the text:

Note You can change the NtfsMFTZoneReservation registry key to increase the volume in Windows NT 4.0 Service Pack 4.

which makes me believe that's the version of Windows this article originally applied to. If you are not using this version this is something that probably has been changed due to the increase of hard disk sizes over the years, and remains undocumented as promised.

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  • So, the percentage could vary from O/S to O/S? Dec 15, 2015 at 19:32
  • @whatever1234566 the percentage isn't relevant. What is relevant, is the allocated space by the MFT and the fact that the size of the MFT is flexible.
    – Mixxiphoid
    Dec 15, 2015 at 19:35
  • I get that, I'm just trying to understand how the MFT Zone is size is calculated upon the initial format, which looks like that it's not necessarily based on 12.5% to start... it could be anything. I also found another article that mentions no percentage: msdn.microsoft.com/en-us/library/windows/desktop/… "The default MFT zone is calculated and reserved by the system when it mounts the volume, and is based on volume size." Dec 15, 2015 at 19:41
  • Just to be clear, it seems this is the right answer because of (1) there is no exact ratio and (2) the edit I made to the initial question that says "reserves approximately." technet.microsoft.com/en-us/library/cc781134(v=ws.10).aspx Dec 15, 2015 at 20:25
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The answer to your question is in the article you refer to.

NTFS reserves 12.5 percent of the volume for exclusive use of the MFT until and unless the remainder of the volume is completely used up. Thus, space for files and directories is not allocated from this MFT zone until all other space is allocated first.

This means that MFT will reserve 12.5% until it needs to be used by the file system. Also, reserved doesn't necessarily mean that it will mark that space as occupied but will be able to claim it easily when needed.
Your MFT could use 200MB because it doesn't need more than that. When it needs to increase, it will use more space from the reserved block (or what is left of it).

To clarify it a bit more, the percentage doesn't really matter. What matters is the disk space that is being used by the MFT and the space available when it needs to grow.
Also, I'm not so sure whether the zones still apply , I had my MFT increased to > 2GB after unpacking 2.6 million files.

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  • If MFT Zone size is say 100MB, after an initial format, then the reserved space is 100MB which should be 12.5% of the volume, but the MFT Zone is not allocated this 100MB space? This is confusing. Dec 15, 2015 at 19:29
  • Why should it allocate if it won't ever use it? If you have 20 big files that fill up your disk, why should the MFT allocate 12.5% to store the references for 20 files? Would be a waste, wouldn't it?
    – Mixxiphoid
    Dec 15, 2015 at 19:33

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