MFT Needs Its Space

Fred: I run Diskeeper 10 to defrag my hard disks and upon completion get the following message: "Due to the high MFT usage, it is recommended that you expand the MFT on this volume. Use the Frag Shield option in the Diskeeper configuration properties to configure this volume to a larger size." I’ve read a few items about changing the MFT and quite frankly it scares me to make changes. Have you had any experience or reports about using the Diskeeper option to modify the MFT? Thanks. —Bob

The Master File Table (MFT) is a database where file and folder metadata— information on size, time and date stamps, permissions and so on— is maintained on NTFS-formatted drives. Every single file on your system has at least one entry. The more files and folders you add to your drive, the larger your MFT becomes. When you delete files, space is made available for re-use in the MFT, but the MFT itself never shrinks.

Because a fragmented MFT is slower than an unfragmented one, some percentage of the drive (12.5% by default) is reserved for the MFT to avoid fragmentation. Each volume of an NTFS drive has two separate areas: a space set aside for the MFT (as well as very small files) and another space for all other files and folders.

If the MFT fills up its own space, the file system will grab more of the "regular" space and assign it to the MFT. Because it’s very unlikely that adjacent space is available, randomly located space will be used for the spill-over MFT, while some part of the MFT remains in the originally allotted space. In other words, the MFT will be divided into more than one piece— it will be fragmented— and your system’s disk access will become slower.

If, on the other hand, the "regular" space fills up with data and applications, the file system will start writing files to the MFT area. As the MFT grows over time, it wil

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Fred Langa

About Fred Langa

Fred Langa is senior editor. His LangaList Newsletter merged with Windows Secrets on Nov. 16, 2006. Prior to that, Fred was editor of Byte Magazine (1987 to 1991) and editorial director of CMP Media (1991 to 1996), overseeing Windows Magazine and others.