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NTFS Compression In Practice

Freeing Up Capacity On An SSD With NTFS Compression
By , Achim Roos

NTFS compression is turned on in just a few clicks:

In Windows Explorer, open the context menu for the system drive or any folder, select its properties, and, in the next window, tick the option "Compress this drive to save disk space" or "Compress contents to save disk space.”. This process can be turned back by simply removing the tick.

With the volume or folder selected, the compression process occurs automatically in the background. Windows reports an error when a file can’t be compressed. Then it gives you the choice to try compressing the file again (which results in the same error message), to cancel, or ignore the message. Because of the number of messages we generated trying to compress the system partition, we ended up picking the fourth option, ignoring all future messages of this kind. The frequency of these messages varies depending on the selected folders. For the Windows directory and its subdirectories, they occur frequently, indicating that system-related files are excluded from NTFS compression.

Once the NTFS compression is completed, the compressed file names are shown in blue in Windows Explorer, easily distinguishing them from the uncompressed folders.

The applications installed on the SSD in our test system were using 70.9 GB of storage space, uncompressed. Rather than select specific folders, we enabled the NTFS compression for the entire system partition, thereby reducing the amount of used space to 58.4 GB (minus 17.8%), and freeing up 12.5 GB with just a couple of mouse clicks.

Comparing the NTFS compression rate with that of other compression tools, the compression performance is rather low, which in turn has a positive impact on the CPU load. Tools like 7-Zip are much more aggressive, and therefore manage to reach higher compression ratios. As an example, the following three folders are packed with 7-Zip on the system partition:

Comptression tool
Original size
Compressed size
Savings in percent
7-ZipProgram Files (x86)17.4 GB10.2 GB40.30%
Program Files 8.5 GB3.1 GB63.50%
Windows15.1 GB3.2 GB78.80%
NTFS Compression
Entire Drive
70.9 GB58.4 GB17.60%
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