NTFS Features

NTFS is Microsoft’s proprietary file system. Read on to learn more about some of the most important NTFS features and how to use them.

File-Based Compression

NTFS supports file compression on an individual file basis. Other programs can read and write NTFS compressed files without having to decompress them first. The decompression process runs in the background and is performed automatically. It might result in a slight slow-down when accessing the files, but on many systems the difference will not be noticeable.

To activate this NTFS feature, simply right-click on a file or folder in the Windows Explorer to open the context menu and select „Properties“. In the next window activate the „Advanced“ options and tick „Compress contents to save disk space“. As long as the box is ticked, the NTFS compression will apply to the file or folder.

Identify NTFS compressed files by their blue file names in the Windows Explorer.

NTFS compression is ideal for some areas, such as:

• Files stored in an uncompressed format (Microsoft Office files, text files, PDF files will yield the best results – already compressed formats like MP3 or JPG files will see little or no decrease in size.)
• Seldomly accessed files (slow-downs will not matter if the file is rarely accessed.)

Microsoft introduced a special NTFS compression for system files with Windows 10. NTFS compression was not recommended for system files in all other Windows versions.

NTFS compression is a great way to save disk space on hard disks.

Permission Management

Another NTFS feature is the setting of access permissions. Permissions are managed via Access Control Lists (ACLs): Such a list contains the permissions attached to each object (such as files and folders). The permissions define which users or processes may access objects and specify which operations they may perform on them.

An example for a typical ACL would be:

User1: read, write; User2: read; User3: read,write

Users 1 and 3 can read and write to the file, User 2 can only read it.

Permissions can depend on parent directories („inherited permissions“) or set for each file („own permissions“). The disk space managers TreeSize and SpaceObServer will list permissions and split the information in inherited and non-inherited NTFS permissions.
<h3″>Alternate Data Streams

On NTFS systems each file consists of different data streams. Imagine the file like a twine consisting of several yarns. One stream contains the security information (for example permissions), another the „real“ file content. User can add additional hidden yarns. These yarns (streams) can contain data, just like the original stream. They are called alternate data Streams (or ADS).

When showing file sizes, the Windows Explorer (as well as many other disk space managers) will show only the main data streams. Thus, one could create a file with an original data stream of 10 MB and add an alternate data stream containing several hundred megabytes of data – for example a 14 GB collection of ripped movies. While users might notice the increase in used disk space, the file itself will remain invisible in the Windows Explorer.

You can easily create an alternate data stream via command line. An example:

echo "ADS" > testfile.txt:hidden-stream

This command line creates the „hidden-stream“ and attaches it to the file „testfile.txt“.

As explained above, the Windows Explorer will only show „testfile.txt“, no matter how big „hidden-stream“ is. Third-party tools like TreeSize or SpaceObServer show the size of all files inlcuding alternate data streams or even specifically search for files containing ADS. They enable you to easily find hidden files on your hard disk.

Hard Links and Symbolic Links

Hard links are a very useful NTFS feature. They can link different directory entries to the same file content. A hard link works just like a file – users will see no difference. Instead of saving the file many times in different folders on the same volume, several hard links can point to the same file content. Changes made to any hard link will affect the file content.

Symbolic links work across several volumes. A symbolic link contains a reference (a path) to another file or folder.

Hard links are are great way to save disk space. They enable users to keep the same file multiple times on their hard disk without having to worry about deleting the main file (which would be the case with symbolic links). TreeSize and SpaceObServer use them to deduplicate files: Files appearing more than once on the same volume are simply replaced by hard links.

Three instances use up the hard disk space one file would occupy.

Disk Space Managers and NTFS

TreeSize Free will display the NTFS compression rate and enable users to apply compression to directory trees. Get TreeSize Professional to gain access to all the NTFS features or test the database-based server space manager SpaceObServer (offers the same NTFS features as TreeSize Professional).