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#1 roy

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Posted 22 December 2013 - 17:46

Hi guys,

I have an external hard drive that I have formatted with exFAT with 128kb allocation unit size.

The contents of the hard drive is about 14GB but it is reported as 51GB (size on disk).

120_GB_1.png

 

120_GB_2.png

What is going on here???
Does this have to do with exFAT?




#2 rippleman

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Posted 22 December 2013 - 18:00

i THINK its like this, not 100% sure though... think of a hard drive having the big plastic totes you can store stuff in. Lets say you have 100 totes but only fill only some completely full and some with only a few things. Whether you fill them up or not, the totes still take up the same space no matter how little you have inside of them. The totes can be thought of allocation size. Your 128 setting is "large" totes. You only have 14 gigs of info in what could possibly hold 51 gigs. If you had smaller totes, the resevered space would be less and less. to  I am not sure on the computer science of what goes in what, how much goes where, or why. This is just my rudimentary understanding of it.



#3 farmeunit

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Posted 22 December 2013 - 18:11

rippleman is most likely correct.  Typically you should just use the defaults.



#4 +snaphat (Myles Landwehr)

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Posted 22 December 2013 - 19:50

In your case you have a cluster size of 128KB and ~323K files. Theoretically, that could yield wasted space of almost ~40GB if you do the math (assuming each file ends on the boundary of a cluster and results in wasting a maximum amount of space). Assuming, I did the math correctly also.

 

It still seems like an odd result to me. I do think it really does have to do with the cluster size though. NTFS normally has a 4KB cluster size which would yield a maximum waste potential of around ~1.2GB for your scenario. So there is a really large difference in the possible waste.

 

EDIT: for clarification, my math is just a multiplication of the file count by the cluster size.



#5 xendrome

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Posted 22 December 2013 - 20:06

My Synology reports this way also... a 980KB jpg file, is showing as 512MB size on disc..

 

See - http://forum.synolog...hp?f=14&t=77073

 

It seems to be an issue with Windows... file system on my Synology is ext4

 

Also see - http://www.dslreport...-Diskq-Anomaly-

 

If you look about 10 posts down, there are 2 images showing the same file, one from Windows 7 view and one from Windows 8.1 view, and Windows 8.1 is clearly showing the large "size on disc" issue for the same file in the same location.



#6 +BudMan

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Posted 24 December 2013 - 12:55

Why did you pick 128Kb for a device its seems your going to store 1000's of little files on? If you were going to say store LARGE files, then ok you might go with something larger then the default.

Your allocation size and number of files is clearly your problem.. Make sure you have backups of these files, then format with the default, and then move your files back.. What do you get then..

#7 Albert

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Posted 24 December 2013 - 13:30

it's known as slack space.

 

imagine your drive as a packing lot. you are only allowed to divide it into a fixed number of similar size, identifiable parking spaces. some spaces are parked efficiently, meaning with vehicles that fully occupied the allocated space. some are packed with smaller motorcycles or even bicycle, i.e. lots of wasted space.

 

your drive properties says 323,703 files. the chances are the more files you have on your drive, the more motorcycles and bicycles will get into the mixes in your parking lot. i.e. more slack space.



#8 +snaphat (Myles Landwehr)

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Posted 24 December 2013 - 18:35

Why did you pick 128Kb for a device its seems your going to store 1000's of little files on? If you were going to say store LARGE files, then ok you might go with something larger then the default.

Your allocation size and number of files is clearly your problem.. Make sure you have backups of these files, then format with the default, and then move your files back.. What do you get then..

 

That's the default size Windows picks for exfat. Unfortunately, it is really giant: http://support.microsoft.com/kb/140365



#9 +BudMan

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Posted 24 December 2013 - 20:58

You know I just plugged in my external and picked format, and went exfat -- and damn it does pick that as default.. That seems stupid if you ask me....

Well good reason not to use that for anything ;)

#10 Torolol

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Posted 24 December 2013 - 21:25

128kB allocation size are utter crap,

heck i formatted my 250GB HDD with 4KB allocation size FAT32.

 

its strange that MSFT KB said 32GB–2TB FAT32 are only 'supported' on NT 3.51

which is weird because i have verified that size up to 512 GB formatted with FAT32 (i don't have larger HDD back then)

can be accessed with no trouble by NT 5.x (2K, XP, 2003)



#11 Torolol

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Posted 24 December 2013 - 21:27

You know I just plugged in my external and picked format, and went exfat -- and damn it does pick that as default.. That seems stupid if you ask me....

Well good reason not to use that for anything ;)

yeah, i never like Windows's default storage formatter 'app'.



#12 +snaphat (Myles Landwehr)

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Posted 24 December 2013 - 21:41

128kB allocation size are utter crap,

heck i formatted my 250GB HDD with 4KB allocation size FAT32.

 

its strange that MSFT KB said 32GB–2TB FAT32 are only 'supported' on NT 3.51

which is weird because i have verified that size up to 512 GB formatted with FAT32 (i don't have larger HDD back then)

can be accessed with no trouble by NT 5.x (2K, XP, 2003)

 

Well, NT 3.51 is really old so I don't think it is too surprising. Only modern OSs natively support larger than 2TB drives and even some backup applications still have issues with larger ones.

 

As for allocation size, it is possible that the 128KB allocation is there for performance reasons with exFat file systems.



#13 The_Decryptor

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Posted 25 December 2013 - 00:37

Strange that exfat ramps up so quickly, I wonder how it would perform if you forced 4KB clusters.

128kB allocation size are utter crap,
heck i formatted my 250GB HDD with 4KB allocation size FAT32.
 
its strange that MSFT KB said 32GB–2TB FAT32 are only 'supported' on NT 3.51
which is weird because i have verified that size up to 512 GB formatted with FAT32 (i don't have larger HDD back then)
can be accessed with no trouble by NT 5.x (2K, XP, 2003)


That's because they want you to use a better filesystem, like NTFS. Give people the ability to make a sub-optimal setup (Like a 2TB FAT32 partition) and they will.



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