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File Size vs. Size on Disk: Why such a difference?

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f0dder:
FAT and NTFS uses the term "cluster size", and multiple files cannot share clusters. NTFS has a size-optimization feature, though, where really-really small files can be stored along with the filesystem metadata about the file.

I guess you have a lot of really small files on that USB stick? Or a ridiculously large cluster size :)

4wd:
More relevant questions are:

How may files are on your USB drive?
What is the cluster size?

For cluster size, the quickest way to find out is to do a Properties on a file whose size is between 1 and 511 bytes and look at the Size on Disk value.

Then multiply the number of files by the cluster size which should give the approximate wasted space due to non-filled clusters.

With flash based devices though, I would have thought you could format with a 512 byte cluster size and experience no noticeable performance hit.  This would minimise space lost.

Edit: Dang that f0dder!  He jumped through a temporal rift and beat me again!

wraith808:
FAT and NTFS uses the term "cluster size", and multiple files cannot share clusters. NTFS has a size-optimization feature, though, where really-really small files can be stored along with the filesystem metadata about the file.

I guess you have a lot of really small files on that USB stick? Or a ridiculously large cluster size :)
-f0dder (April 07, 2010, 05:55 PM)
--- End quote ---

But does that work on flash drives?  I know that fixed drives use that, but I thought that flash drives didn't allow that for speed considerations?

MilesAhead:
Just open a dos prompt, change to the usb drive and run
chkdsk

It will show the bytes per allocation unit.
My usb stick is formatted NTFS and shows 4096

xtabber:
Don't know about Linux, but in Windows, you can use Treesize from JAM Software to find out exactly how much space is used/wasted by files on any FAT or NTFS formatted drive and how that would change under different cluster sizes. Treesize Pro has long been one my most often used utilities (it does a lot more than that), but I think the free version will give you the information you want.

Treesize free is at http://www.jam-software.com/freeware/index.shtml .

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