Defragmentation - Approach and Defragmenters By File-system Type

Approach and Defragmenters By File-system Type

• FAT: MS-DOS 6.x and Windows 9x-systems come with a defragmentation utility called Defrag. The DOS version is a limited version of Norton SpeedDisk. The version that came with Windows 9x was licensed from Symantec Corporation, and the version that came with Windows 2000 and XP is licensed from Condusiv Technologies.
• NTFS was introduced with Windows NT 3.1, but the NTFS filesystem driver did not include any defragmentation capabilities. In Windows NT 4.0, a few defragmenting APIs were introduced that third-party tools could use to perform defragmentation tasks; however, no defragmentation software was included. In Windows 2000, Windows XP and Windows Server 2003, Microsoft included a defragmentation tool based on Diskeeper that made use of the defragmentation APIs and was a snap-in for Computer Management. In Windows Vista, Windows 7 and Windows 8, Microsoft appears to have written their own defragmenter which has no visual diskmap and is not part of Computer Management. There are also number of free and commercial third-party defragmentation products are available for Microsoft Windows.
• BSD UFS and particularly FreeBSD uses an internal reallocator that seeks to reduce fragmentation right in the moment when the information is written to disk. This effectively controls system degradation after extended use.
• Linux ext2, ext3, and ext4: Much like UFS, these filesystems employ allocation techniques designed to keep fragmentation under control at all times. As a result, defragmentation is not needed in the vast majority of cases. ext2 uses an offline defragmenter called e2defrag, which does not work with its successor ext3. However, other programs, or filesystem-independent ones, may be used to defragment an ext3 filesystem. ext4 is somewhat backward compatible with ext3, and thus has generally the same amount of support from defragmentation programs. In practice there are no stable and well-integrated defragmentation solutions for Linux, and thus no defragmentation is performed.
• VxFS has the fsadm utility that includes defrag operations.
• JFS has the defragfs utility on IBM operating systems.
• HFS Plus (Mac OS X) introduced in 1998 a number of optimizations to the allocation algorithms in an attempt to defragment files while they are being accessed without a separate defragmenter. If the filesystem becomes fragmented, the only way to defragment it is to use a utility such as Coriolis System's iDefrag, or to wipe the hard drive completely and install the system from scratch.
• WAFL in NetApp's ONTAP 7.2 operating system has a command called reallocate that is designed to defragment large files.
• XFS provides an online defragmentation utility called xfs_fsr.
• SFS processes the defragmentation feature in almost completely stateless way (apart from the location it is working on), so defragmentation can be stopped and started instantly.