NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7.
NTFS supersedes the FAT file system as the preferred file system for Microsoft’s Windows operating systems. NTFS has several improvements over FAT and HPFS (High Performance File System) such as improved support for metadata and the use of advanced data structures to improve performance, reliability, and disk space utilization, plus additional extensions such as security access control lists (ACL) and file system journaling.
History
In the mid 1980s, Microsoft and IBM formed a joint project to create the next generation graphical operating system. The result of the project was OS/2, but eventually Microsoft and IBM disagreed on many important issues and separated. OS/2 remained an IBM project. Microsoft started to work on Windows NT. The OS/2 filesystem HPFS contained several important new features. When Microsoft created their new operating system, they borrowed many of these concepts for NTFS.. Probably as a result of this common ancestry, HPFS and NTFS share the same disk partition identification type code (07). Sharing an ID is unusual since there were dozens of available codes, and other major filesystems have their own code. FAT has more than nine (one each for FAT12, FAT16, FAT32, etc.). Algorithms which identify the filesystem in a partition type 07 must perform additional checks. It is also clear that NTFS owes some of its architectural design to Files-11 used by VMS. This is hardly surprising since Dave Cutler was the main lead for both VMS and Windows NT.
Versions
NTFS has five released versions:
- v1.0 with NT 3.1, released mid-1993
- v1.1 with NT 3.5, released fall 1994
- v1.2 with NT 3.51 (mid-1995) and NT 4 (mid-1996) (occasionally referred to as "NTFS 4.0", because OS version is 4.0)
- v3.0 from Windows 2000 ("NTFS V5.0")
- v3.1 from Windows XP (autumn 2001; "NTFS V5.1"), Windows Server 2003 (spring 2003; occasionally "NTFS V5.2"), Windows Vista (mid-2005) (occasionally "NTFS V6.0") and Windows Server 2008
V1.0 and V1.1 (and newer) are incompatible: that is, volumes written by NT 3.5x cannot be read by NT 3.1 until an update on the NT 3.5x CD is applied to NT 3.1, which also adds FAT long file name support. V1.2 supports compressed files, named streams, ACL-based security, etc. V3.0 added disk quotas, encryption, sparse files, reparse points, update sequence number (USN) journaling, the $Extend folder and its files, and reorganized security descriptors so that multiple files which use the same security setting can share the same descriptor. V3.1 expanded the Master File Table (MFT) entries with redundant MFT record number (useful for recovering damaged MFT files).
Windows Vista introduced Transactional NTFS, NTFS symbolic links, partition shrinking and self-healing functionality though these features owe more to additional functionality of the operating system than the file system itself.
Features
NTFS v3.0 includes several new features over its predecessors: sparse file support, disk usage quotas, reparse points, distributed link tracking, and file-level encryption, also known as the Encrypting File System (EFS).
USN Journal
The USN Journal is a system management feature that records changes to all files, streams and directories on the volume, as well as their various attributes and security settings.
It is a critical functionality of NTFS (a feature that FAT/FAT32 does not provide) for ensuring that its internal complex data structures (notably the volume allocation bitmap, or data moves performed by the defragmentation API, the modifications to MFT records such as moves of some variable-length attributes stored in MFT records and attribute lists, or updates to the shared security descriptors, or to the boot sector and its local mirrors where the last USN transaction committed on the volume is stored) and indices (for directories and security descriptors) will remain consistent in case of system crashes, and allow easy rollback of uncommitted changes to these critical data structures when the volume will be remounted.
In later versions of Windows, the USN journal has since then extended to trace the state of other transactional operations on other parts of the NTFS filesystem, such as the VSS shadow copies of system files with copy-on-write semantics, or the implementation of Transactional NTFS and of distributed filesystems (see below).
Hard links and short filenames
Originally included to support the POSIX subsystem in Windows NT, hard links are similar to directory junctions, but used for files instead of directories. Hard links can only be applied to files on the same volume since an additional filename record is added to the file's MFT record. Short (8.3) filenames are also implemented as additional filename records that don't have separate directory entries. Hard links also have the behavior that changing the size or attributes of a file may not update the directory entries of other links until they are opened.
Alternate data streams (ADS)
Alternate data streams allow more than one data stream to be associated with a filename, using the filename format "filename:streamname" (e.g., "text.txt:extrastream"). Alternate streams are not listed in Windows Explorer, and their size is not included in the file's size. Only the main stream of a file is preserved when it is copied to a network share or FAT-formatted USB drive, attached to an e-mail, or uploaded to a website. As a result, using alternate streams for critical data may cause problems. NTFS Streams were introduced in Windows NT 3.1, to enable Services for Macintosh (SFM) to store Macintosh resource forks. Although current versions of Windows Server no longer include SFM, third-party Apple Filing Protocol (AFP) products (such as Group Logic's ExtremeZ-IP) still use this feature of the file system.
Malware has used alternate data streams to hide its code; some malware scanners and other special tools now check for data in alternate streams. Microsoft provide a tool called Streams to allow users to view streams on a selected volume.
Very small ADS are also added within Internet Explorer (and now also other browsers) to mark files that have been downloaded from external sites: they may be unsafe to run locally and the local shell will require confirmation from the user before opening them. When the user indicates that he no longer wants this confirmation dialog, this ADS is simply dropped from the MFT entry for downloaded files.
Some media players have also tried to use ADS to store custom metadata to media files, in order to organize the collections, without modifying the effective data content of the media files themselves (using embedded tags when they are supported by the media file formats such as MPEG and OGG containers); these metadata may be displayed in the Windows Explorer as extra information columns, with the help of a registered Windows Shell extension that can parse them, but most media players prefer to use their own separate database instead of ADS for storing these information (notably because ADS are visible to all users of these files, instead of being managed with distinct per-user security settings and having their values defined according to user preferences).
Sparse files
Sparse files are files which contain sparse data sets, data mostly filled with zeros. Database applications, for instance, sometimes use sparse files. Because of this, Microsoft has implemented support for efficient storage of sparse files by allowing an application to specify regions of empty (zero) data. An application that reads a sparse file reads it in the normal manner with the file system calculating what data should be returned based upon the file offset. As with compressed files, the actual sizes of sparse files are not taken into account when determining quota limits.
File compression
NTFS compresses files using a variant of the LZ77 algorithm. Although read–write access to compressed files is transparent, Microsoft recommends avoiding compression on server systems and/or network shares holding roaming profiles because it puts a considerable load on the processor.
Volume Shadow Copy
The Volume Shadow Copy Service (VSS) keeps historical versions of files and folders on NTFS volumes by copying old, newly-overwritten data to shadow copy ( copy-on-write ). The old file data is overlaid on the new when the user requests a revert to an earlier version. This also allows data backup programs to archive files currently in use by the file system. On heavily loaded systems, Microsoft recommends setting up a shadow copy volume on a separate disk. To ensure consistent recovery in case of system crashes, the VSS also uses the USN journal to mark local transactions and ensure that committed changes to the system files will be effectively recovered after system restart when the NTFS volume will be remounted, or safely rolled back to an older version if the new version was not fully recorded before actual commits before closing the modified file. However, these VSS shadows are not coordinated globally on multiple files or volumes, except when using a transaction coordinator (see below). They can just be used to ensure that older versions will remain accessible during backup operations, for getting consistent system images in those backups
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