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To Compress or not to compress

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Cpilot:
Just out of curiosity, how do you all feel about compressing your main drives?
Does everyone do it?
Any pros and most importantly cons?
I can google around I suppose and get opinions but I was wondering how folks here feel about it.

f0dder:
Afaik there's no "full drive compression" with NTFS, pretty much died out with stacker/doublespace back in the DOS days. NTFS does support per-file compression though, and it can be inheritable for directory structures - so in theory I guess it could be applied automatically for a whole drive.

I only use it selectively, though, since some data just doesn't compress well, and your boot files must NOT be compressed (or NTFS-encrypted, for that matter). Theoretically, with a fast CPU, it can be an advantage on some types of files, because systems are often disk I/O limited. Source code (mainly static stuff like the huge collection of PlatformSDK headers) compress pretty well...

In reality, however, I haven't seen much speed improvement from this. It might help with the initial build of a program after a cold boot, but after that, the necessary files tend to be in filesystem cache, and the disk isn't involved at all. Also, you don't gain that much disk space from the compression, and drives are cheap these days. Last, iirc there's some fragmentation-related issues once you enable NTFS compression, but I can't remember the details and I'm not in the mood for googling it up  :)

Cpilot:
Last, iirc there's some fragmentation-related issues once you enable NTFS compression, but I can't remember the details and I'm not in the mood for googling it up 
--- End quote ---
No biggy, like I said, just interested in the users here.
I can google around also but I'm more interested in personal takes on it.

Lashiec:
I only compress loose files in ZIP or RAR format, though the perspective of compressing the entire drive(s) look tempting, it's not that I'm dying for that extra free space. I guess Microsoft feels the same, as that particular option was never featured as "ZOMG! Look at this". BTW, does anyone know what are the savings compared to traditional algorithms (on the same files that is?

Afaik there's no "full drive compression" with NTFS, pretty much died out with stacker/doublespace back in the DOS days. NTFS does support per-file compression though, and it can be inheritable for directory structures - so in theory I guess it could be applied automatically for a whole drive.
-f0dder (May 14, 2008, 09:28 PM)
--- End quote ---

Then what about the first checkbox:


that reads "Compress contents to save disk space"?

f0dder:
NTFS compression uses a LZW variant, so I guess it's roughly comparable to .zip - too lazy to test, though. The format-time option probably just sets a flag in the volume header saying that "by default, every file on this volume will be compressed" - the compression certainly is file-based (but again, it is inheritable on folders - ie., if you mark a folder for compression, new files and folders created in there will automatically be compressed).

Now, think about what happens for non-static files... if you want to write some data in the middle of a file. NTFS compresses in cluster sizes  (and only works with cluster sizes of <= 4kb) - changing the data in a cluster could mean it will now take two clusters after compression, instead of a single one. What does this do for fragmentation? :)

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