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Disk Uses More Space Than Size of Files



 
 
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Old October 21st 13, 09:37 PM posted to microsoft.public.windowsxp.hardware
Paul
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Posts: 18,275
Default Disk Uses More Space Than Size of Files

W wrote:
"VanguardLH" wrote in message
...
"VanguardLH" wrote ...
In addition, Windows Explorer will never show you the size of Alternate
Data Streams (ADS) added to a file. For example, I can create a .txt
file whose primary data stream chews up only, say 5KB but then add an
alternate data stream that is gigabytes in size. Windows Explorer,
'dir', and other normal file utilities will only show you the size of
the primary data stream.

http://en.wikipedia.org/wiki/Alterna...ream#Microsoft


http://www.symantec.com/connect/arti...e-data-streams

I found a better utility for scanning for ADS: NirSoft
AlternateStreamView. Strangely, this utility does not agree on all of the
results with the ADS Scanner you mentioned.

Some surprising things I found:

1) Dropbox is using the ADS feature actively, and many dropbox files have up
to 4096 bytes of ADS information attached to them.

2) The AlternateStreamView shows an additional field of
"StreamAllocatedSize". In my boot partition I had a few files where the
actual ADS stream was about 1K but the ADS Allocated Size was about 65K.
Does anyone know if the "allocated size" represents actual disk space in
use?

Most of these files that AlternateStreamView reported large allocation sizes
on were not even seen by ADS Scanner.


Amazingly, it notes that concept here. That StreamAllocatedSize is set aside
for the stream for some reason. I don't know if this idea is intended for
sparse storage, or what they were thinking. You would have thought, if they
were going to waste space, they'd round to the nearest 4K or whatever.

http://msdn.microsoft.com/en-us/libr...(v=vs.85).aspx

For a stream to work, it would have to have a provision for extending the
storage space later (leading to fragmentation). Pre-allocating a space,
isn't of much use if you don't "guess right" on the size to set aside.
So I'm missing what the big gain is, in having such a feature.

Paul
 




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