MFT Fragmentation
Fragmentation of the Master File Table (MFT) can be a serious problemon NTFS partitions. This is because the MFT is used for every disk I/O. While much of the MFT can be cached, sothat an actual disk I/O does not have to be done every time, it is still true that on most systems the MFT is accessedmore than any other file. This means that MFT fragmentation is likely to have more impact on the system than fragmentationof any other single file. Until Diskeeper is capable of defragmenting the MFT, steps should be taken to prevent,or at least minimize, MFT fragmentation. But how does the MFT get fragmented in the first place?
Converting FAT to NTFS
When a FAT partition is converted to NTFS, an MFT is created. If thereis a large enough contiguous free space, the MFT is made contiguous, with contiguous pre-allocated expansion space.However, since the pre-allocation comprises about 12% of the partition, this is usually not possible, and the MFTis created fragmented. In addition, the MFT will almost certainly not be at the beginning of the disk, where itis put on partitions that are created with the NTFS format. This means that you have data areas before the MFTand after it, then a secondary copy of critical MFT data, then another data area. So you can see that the convertedpartition has three data areas instead of the usual two; data fragmentation will thus begin sooner.
The problem for the MFT is that Windows NT will, under some conditions,write files in the space reserved for MFT expansion. If such a file has been written, then as the MFT grows, whenit reaches the file, the MFT will have to fragment to get around the file.
Note that the system partition created on installing Windows NT isa FAT partition. If, during installation, you choose to use the NTFS format, the partition will still be createdas FAT, and only converted to NTFS after the first boot. This means you get the initial system files written tothe beginning of the disk, then, when the conversion is done, the MFT is created. You can avoid this by using adual-boot system (see the earlier article on dual boot for details). Basically, you install a minimal Windows NT,then create an NTFS partition, preferably on another disk, and do your full installation of Windows NT to the newpartition. Afterwards you can reformat the original partition to NTFS and reinstall the minimal Windows NT to retainthe benefits of having two Windows NT installations.
MFT Record Overflow
A partition can have scattered pieces of the MFT sitting in the dataarea, outside the normal MFT area (the part that Diskeeper shows as green). These "MFT record overflow"pieces are actually things like extent lists, security attributes, and extremely long filenames that at some timein the past couldn't fit inside the MFT record. These pieces are not part of a file, but are extensions to theMFT. Thus Diskeeper currently cannot move them. This means the free space cannot be fully consolidated, and itwill be much harder for the partition to be defragmented.
Preventing MFT Fragmentation
The only real "fix" at this time is to back up the partition,reformat it, and restore the data. Note that the partition should have a cluster size of at least one kilobyte,because the MFT records are one kilobyte in size; a smaller cluster size will allow the MFT records themselvesto fragment. To prevent or minimize MFT fragmentation, you should avoid the following:
- converting FAT partitions to NTFS format (other than by deletingand recreating the partition)
- use of compressed files on an active partition
- compressing and decompressing entire volumes or directory sub-trees
- unnecessary security lists
- extremely long file and directory names (more than 31 characters).
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