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NTFS Drives |
  
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NTFS Drives |
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The file system NTFS can be used with the operating system Windows NT or later. It offers some special features which also have effects for SpaceObServer. We will describe some of these features and their impacts on this software in the following paragraphs.
Access Control Lists
A user under Windows NT/2000 can restrict the way other users can access his files and folders. He can grant or deny other users or groups certain rights like reading, writing, executing or deleting files. That way a user can even deny the administrator rights to access his files and folders. If an administrator tries to access a folder in the Explorer, to which the owner denied any other users read access, an "Access Denied" error message will be displayed. However, SpaceObServer is able to scan such folders, if you are logged in as administrator or as a user that has the right to perform backups (This option can be changed at "Control Panel > Administrative Tools > Local Security Policy" under Windows 2000).
NTFS supports compression on a single file basis. Files that are compressed on a NTFS volume can be read and written without first being decompressed by another program. Decompression happens automatically while reading the file. The file is compressed again when it is closed or explicitly saved.
The space occupied by a compressed file is usually much smaller than its normal size. As a consequence for folders that are partially or completely compressed, the allocated space reported by SpaceObServer> may be smaller than the size reported for this folder.
The NTFS version that comes with Windows 2000 supports an additional concept, that is similar to compressed files: sparse files. Files which are large but only partially used are called sparse files. Because the operating system does not allocate disk space for the unused parts of a sparse file, it occupies less disk space than its mentioned size. SpaceObServer treats sparse files like compressed files and also calculates the compression ratio for them. Compressed files/folders are shown blue in the Details view.
SpaceObServer is able to compress and decompress entire file system branches using the context menu.
Reparse Points: Volume Mount Points and Symbolic Links
Since Windows 2000 NTFS supports volume mount points and symbolic links. A volume mount point is an existing path where you "mount" another volume. Given this, users and applications can refer to the mounted volume by that path. It allows you to unify disparate file systems into one logical file system. Symbolic links work similar: e.g. if you have an empty folder C:\Documents\Images, you can create a symbolic link to E:\Pics in it. Applications will then see the content of E:\Pics in C:\Documents\Images.
If you have activated the scan option "Follow Mount Points and Symbolic Links" in the Configure Scans dialog, SpaceObServer will include the contents of these folders when scanning. You can exclude the Mount Points from the reports by activating the option "Exclude Mount Points" in the SpaceObServer file search. Since they are not physically stored on the drive you are scanning, this may produce irritating results.
Change Journals:
The change journal provides a persistent log of changes made to files on a volume. NTFS uses the change journal to track information about added, deleted, and modified files for each volume. The change journal describes the nature of any changes to files on the volume. Anytime a file or folder is created, modified, or deleted, NTFS adds a record to the change journal for that volume.
SpaceObServer can uses the information stored in the NTFS Change Journal to update the file system information. You can activate the usage of Change Journals in the Configure Scan dialog (Scan > Configure Scans > Update Options) by checking the 'Use NTFS Change Journal' option.
Note: Change Journals are available for local NTFS drives only. They will be activated for a complete drive.
In NTFS, a file consists of different data streams. One stream holds the security information (access rights and such things), another one holds the "real data" you expect to be in a file. There may be alternate data streams, holding data the same way the standard data stream does. These alternate data streams are hidden. That means that you can have a file with 1 byte in the official main data stream and some hundred MB in one or more alternate data streams. The dir command, file managers or Windows Explorer will show 1 byte as the size of this file, but it actually allocates more space on your hard drive.
SpaceObServer can detect alternate data streams and add their sizes to the allocated file size.
Note: ADS stores information in the same cluster as the main data stream, so if a file has one or more ADS, this file does not necessarily allocate more disk space.
You can choose to detect Alternate Data Streams and hard links, to get a more accurate allocated space of directory branches, within the 'Configure Scans' dialog (Scan > Configure Scans > Scan Options). This option is deactivated by default, because it slows down the scan performance.
In a Windows environment a hard link is a reference, or pointer, to physical data on a NTFS storage volume. All named files are hard links. The name associated with the file is simply a label that refers the operating system to the actual data. On NTFS volumes more than one name can be associated with the same data. Though called by different names, any changes made will affect the actual data, regardless of how the file is called at a later time. Hard links can only refer to data that exists on the same file system. The data is accessible as long as at least one link that points to it exists. When the last link is removed, the space is considered free.
If more than one hard link points to a file's data, the space allocated by these files is just one time the file size (not including the space of the file master table). No matter how many hard links exist, SpaceObServer is able to detect the number of hard links pointing to one file data and takes that value into account when calculating the allocated space of directory branches.
You can choose to detect hard links and Alternate Data Streams, to get a more accurate allocated space of directory branches, within the 'Configure Scans' dialog (Scan > Configure Scans > Scan Options). This option is deactivated by default, because it slows down the scan performance.