Sunday, April 1, 2012

What is MFT?

NTFS is a new file system adopted by Windows NT and it has many new features. In NTFS, all data stored in volumes are contained in the file named $MFT (Master File Table). And $MFT consists of File Record array. The size of File Record is fixed, usually 1KB. It is like inode in Linux. File Record in $MFT file is physically continuous and identified from number 0. File System itself only applies $MFT for fsystem organization and framework, which is called Metadata in NTFS. And in NTFS File System, all things in disk are shown in the form of files. Even Metadata are stored in the form of a set of files.

Master File Table (MFT) is index of every file in the volume. It records "attributes" of every file and every attribute contains different types of information. Therefor, enough space must be left for MFT. In NTFS, MFT plays an important role and it has great influence on volumes. MFT is accessed frequently in the process of system space allocation and disk read-write.that why it is has an important influence on volumes in NTFS. A specific location is obligated nearby MAT to reduce fragments in MAT. It takes up 12.5% of volume in default state. Although this location can furthest reduce fragments, it is not always suitable.

If users want to manage MFT space, NtfsMftZoneReservation of REG_DWORD can be added in HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control \FileSystem. Its default-value is 1, varing from 1-4(1 means 12.5% of volume, 2meaans 25%, 3means 37.5% and 4 means 50%).

NTFS contains a Master File Table (MFT). MFT is an index file mapping all the objects in disk. In MFT, every file including MFT has one mapping at least in NTFS disk. Size, time and timestamp, security attribute and data location are contained in MFT.  

Once fragments appear in MFT, Disk Defragmenter can not be used. However, MFT can be used continuously to access other files in disk, and this also causes fragment, so access time becomes longer and disk performance is lower. In NTFS, 1/8 of disk space is specifically used for MFT, leading to a lowest influence. When MFT expands, this area (MFT aera) can keep continuity of MFT as much as possible.

No comments:

Post a Comment