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I'm testing Windows 10 and one very interesting thing I found is new switches for compact:

Displays or alters the compression of files on NTFS partitions.

COMPACT [/C | /U] [/S[:dir]] [/A] [/I] [/F] [/Q] [/EXE[:algorithm]]
    [filename [...]]

<cut>

  /EXE      Use compression optimized for executable files which are read
    frequently and not modified.  Supported algorithms are:
    XPRESS4K  (fastest) (default)
    XPRESS8K
    XPRESS16K
    LZX       (most compact)

I've conducted an experiment:

compression type        | size (bytes)
––––––––––––––––––––––––+–––––––––––––
pre-win10:
no compression          |  46 652 204
LZNT1 (NTFS default)    |  26 230 789

new ones:
LZX                     |  15 749 125
XPRESS16K               |  20 094 981
XPRESS8K                |  21 131 269
XPRESS4K (/EXE default) |  23 011 333

non-transparent archivers:
7z 9.38 -tzip -mx=9     |  15 254 240
7z 9.38 -t7z -mx=9      |   7 522 003

as you can see, /EXE:LZX does really good, and, comparing to zip, there's no real tradeoff anymore by compression ration, but NTFS compression has much better availability (it's on-line).

Unfortunately (but unsurprisingly), these files cannot be opened on Windows 8.1 or any previous ones (checked it).

So, my question is, how to decompress files compressed with these "new methods" on previous Windowses? Just copying compact.exe from latest Windows 10 build does not work, unfortunately (but, again, unsurprisingly).

If there's none, then these new methods are basically limited to internal disk, and I'll need bootable Windows 10 media for files salvaging (in emergency).

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  • you can't. Use a Windows 10 ISO to boot into the recovery tools/cmd.exe and run the compact command. Apr 29, 2015 at 17:41
  • I can even write win10 to-go bootable flash with Rufus. Still requirement to boot something to decompress a file feels somewhat unnatural. Apr 29, 2015 at 21:14
  • 2
    it's a new feature of Win10, so it requires Win10 to use it. May 1, 2015 at 8:36
  • well, I'm not about fully using this "feature", I'm about data preservation. With no way to decompress data outside of windows 10, I'll rather not use this feature in windows 10 altogether except for the fixed system disk! Because in case I will have no Windows 10 at hand, I won't be able to access my data. @magicandre1981 May 1, 2015 at 9:31
  • 1
    More information here
    – Moab
    Jul 6, 2015 at 17:20

1 Answer 1

3

These new compression methods are (claimed to be) implemented outside of NTFS, implemented as reparse points - leaving it to new (for Windows 10/Server 2016) filesystem filter driver(s) to handle them.

System compression, also known as "Compact OS", is a Windows feature that allows rarely modified files to be compressed using the XPRESS or LZX compression formats. It is not built directly into NTFS but rather is implemented using reparse points. This feature appeared in Windows 10 and it appears that many Windows 10 systems have been using it by default.

This repository contains a plugin which enables the NTFS-3G FUSE driver to transparently read from system-compressed files. It must be built against NTFS-3G version 2016.2.22AR.1 or later, since that was the first version to include support for reparse point plugins.

ntfs-3g-system-compression - README.md

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  • hm, interesting. I'm eager seeing it merged to main ntfs-3g codebase, so any Linux distributive could read the files. Great! Dec 8, 2016 at 18:58
  • @Mike - In the future please quote and cite all relevant information from links you provide in your answers.
    – Ramhound
    Dec 8, 2016 at 19:35

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