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I have a process where I am removing BLOBs from a DB and writing them to a file structure on disk. I have a 1TB disk, with a single folder in the root, and a structure similar to:


There will be potentially several thousand 'file.txt's in the same folder, but the average appears to be about 300. I ran my export program for 10,000 records to gather metrics, and now have concerns.

Each file.txt is compressed with DeflateStream, and appears to average about 900 bytes. The disk was formatted NTFS with 2k clusters, and 8dot3 filenames disabled. Though, based on the attached screenshot, each file is taking 8192 bytes instead of 2048 like I would expect. I have over 75 million files to write, and we add about 3 million a week, so disk space usage is something that needs to be addressed.

So, my question:

Why is each file taking 8kb even though I used 2kb clusters when formatting?

enter image description here

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This is an average check; can you confirm this by verifying a given file? – lserni Apr 11 '13 at 21:06
@Iserni: Each file is an XML document that averages 4700 bytes before compression. The after-compression size for each one is anywhere from 800 bytes to 1600 bytes. I spot-checked about 30. The pattern scales too -- 60GB used at 7 million files, while only about 7GB is reported for "size". – insta Apr 11 '13 at 21:12
After checking out the relevant TechNet article (, I admit to being baffled. Can you add the output of the fsutil fsinfo ntfsinfo f: command? – lserni Apr 11 '13 at 21:34
Did you verify that you actually got the 8k cluster size that you thought you selected? Open notepad type "x" and save the file how big is this file? – cybernard Apr 11 '13 at 22:32

This resolved itself. It took some combination of creating and resizing volumes in Disk Management, reformatting with different cluster sizes, and throwing goat bones. I can't say I could determine the actual cause, and several coworkers stood behind me in disbelief as I went through the steps.

Iserni: it now reports 2k clusters like it should cybernard: the file was actually showing 8192 bytes on disk while this was going on.

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