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USN_JOURNAL_DATA_V0 structure

Represents an update sequence number (USN) change journal, its records, and its capacity. This structure is the output buffer for the FSCTL_QUERY_USN_JOURNAL control code. Prior to Windows 8 and Windows Server 2012 this structure was named USN_JOURNAL_DATA. Use that name to compile with older SDKs and compilers.

Syntax


typedef struct {
  DWORDLONG UsnJournalID;
  USN       FirstUsn;
  USN       NextUsn;
  USN       LowestValidUsn;
  USN       MaxUsn;
  DWORDLONG MaximumSize;
  DWORDLONG AllocationDelta;
} USN_JOURNAL_DATA_V0, *PUSN_JOURNAL_DATA_V0, USN_JOURNAL_DATA, *PUSN_JOURNAL_DATA;

Members

UsnJournalID

The current journal identifier. A journal is assigned a new identifier on creation and can be stamped with a new identifier in the course of its existence. The NTFS file system uses this identifier for an integrity check.

FirstUsn

The number of first record that can be read from the journal.

NextUsn

The number of next record to be written to the journal.

LowestValidUsn

The first record that was written into the journal for this journal instance. Enumerating the files or directories on a volume can return a USN lower than this value (in other words, a FirstUsn member value less than the LowestValidUsn member value). If it does, the journal has been stamped with a new identifier since the last USN was written. In this case, LowestValidUsn may indicate a discontinuity in the journal, in which changes to some or all files or directories on the volume may have occurred that are not recorded in the change journal.

MaxUsn

The largest USN that the change journal supports. An administrator must delete the change journal as the value of NextUsn approaches this value.

MaximumSize

The target maximum size for the change journal, in bytes. The change journal can grow larger than this value, but it is then truncated at the next NTFS file system checkpoint to less than this value.

AllocationDelta

The number of bytes of disk memory added to the end and removed from the beginning of the change journal each time memory is allocated or deallocated. In other words, allocation and deallocation take place in units of this size. An integer multiple of a cluster size is a reasonable value for this member.

Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

WinIoCtl.h (include Windows.h)

See also

Volume Management Structures
FSCTL_QUERY_USN_JOURNAL

 

 

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