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One of a our file servers at work is being compressed with NTFS compression. I've read about it being generally inadvisable on servers. But I've not found anything the states where the compression/decompression is done.

On a mapped network drive does the decompression happen using the server cpu resources, or the local client's?

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up vote 3 down vote accepted

According to the book "Microsoft Windows Server 2003: Delta Guide" (the top of page 33, compressed folders) the compression and decompression is done on the Server:

Another drawback to NTFS compression is that, because it is a file system attribute, it is compressed only on the file system. The implication of this is that, if you access the file across the network, it is first uncompressed by the operating system and then sent across the network in an uncompressed format. Thus, no network bandwidth improvement occurs because the file is sent across the network as if it were never compressed.

I've not (yet) found a Microsoft web page stating it that clear.

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Compressed folders are no different than any other compressed file. Like a .zip file, you can see the contents, but you cannot work with them until they are uncompressed. – Keltari May 13 '13 at 14:16
@Keltari: I guess you comment because I wrote "(page 33, compressed folders)"? "compressed folders" is the name of the chapter. And besides, compressed files are compressed on disc. Compressed folders are regular Folders with just one bit more set in the attributes. Compressed Folders are themselves not compressed, only the files in the compressed Folders are compressed. – Werner Henze May 14 '13 at 8:10

When you copy or move a compressed NTFS file to a different folder, NTFS decompresses the file, copies or moves the file to the new location, and then recompresses the file. This behavior occurs even when the file is copied or moved between folders on the same computer. Compressed files are also expanded before copying over the network, so NTFS compression does not save network bandwidth.

So all decompression happens on the machine having the compressed drive every time data is read off the drive.

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sorry but it doesn't really, I was looking for something less ambiguous. – cjb110 May 13 '13 at 13:17

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