The USN Journal (Update Sequence Number Journal), or Change Journal,
is a feature of the Windows NT file system (
NTFS
NT File System (NTFS) (commonly called ''New Technology File System'') is a proprietary journaling file system developed by Microsoft in the 1990s.
It was developed to overcome scalability, security and other limitations with File Allocation Tabl ...
) which maintains a record of changes made to the
volume
Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
. It is not to be confused with the journal used for the
NTFS file system journaling.
When
Windows 2000
Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...
was released,
Microsoft
Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...
created NTFS version 3.0, which included several new features and improvements over older versions of the
file system. One of these was a new system management feature that is very useful for certain types of
applications. Under Windows 2000, NTFS 3.0
partitions can be set to keep track of changes to files and directories on the volume, providing a record of when and what was done to the various objects. When enabled, the system records all changes made to the volume in the USN Journal, which is the name also used to describe the feature itself.
One journal is maintained for each NTFS volume and stored in the
NTFS metafile named $Extend\$UsnJrnl. It begins as an empty
file. Whenever a change is made to the volume, a record is added to the file. Each record is identified by a
64-bit
In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit central processing units (CPU) and arithmetic logic units (ALU) are those that are based on processor registers, a ...
Update Sequence Number or USN (for this reason Change Journals are sometimes called USN Journals). Each record in the Change Journal contains the USN, the name of the file, and information about what the change was.
The Change Journal describes the changes that took place using bit flags (e.g. USN_REASON_DATA_OVERWRITE
), therefore it does not include all the
data
Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...
or details associated with the change. For this reason the Change Journal cannot be used to undo operations on files within NTFS.
Uses
The USN Journal is used by the
File History feature introduced in
Windows 8
Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on August 1, 2012, made available for download via Microsoft ...
to determine which files have changed since the last backup so that only files that have changed are added to the history. The
desktop search utility
Everything
Everything, every-thing, or every thing, is all that exists; it is an antithesis of ''nothing'', or its complement. It is the totality of things relevant to some subject matter. Without expressed or implied limits, it may refer to . The uni ...
monitors the journal to update its database of file names.
References
External links
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{{DEFAULTSORT:Usn Journal
Computer file systems
Windows disk file systems