2 drives - same files - different "Used Space"

I have 2 identical external hard drives (Western Digital 2tb My Passport) and I copied all the data from 1 drive to the other. When I check the properties of the files the sizes match, but when I check the properties of the drives the used space differs by ~4mb. I've been checking the MD5 hash data of my bigger files and so far there are no differences. uTorrent's hash check (force recheck) also says the files are ok.

Here is a picture of my problem: http://i.imgur.com/btoFWII.png

-both drives are formatted the same (NTSF, same cluster size)
-Crystal Disk Info and Windows Error Check both say that the drives are fine
-There were no vibrations that might disrupt the drives when copying. I wasn't even using the computer.
-There are no hidden files in either drive

Can anyone explain this 4mb size difference?

 

Not all drives are created equal, there are always small differences in capacity, manufacturing process error margin, that's all it is.

 

Exactly. So it's not a "problem" intrinsically, and you will notice +/- differences in another "identical" hard drive as well. Also, a lot of people get hung up on the advertised capacity, but remember, 1 TB = 1024 GB =1048576 MB =1073741824 KB =1099511627776 bytes

or

1 TB = 2^10 GB = 2^20 MB =2^30 KB =2^40 bytes (I think. Someone correct my math if I'm off).

 

This is not a matter of marketed capacity vs formatted capacity, or counting in base 10 vs base 2 if you prefer, although that does come into play a little. If you take the example of a 1 TB drive, manufacturers can't put 10^12 Bytes with 100% accuracy on the drive, there's always a little more or a little less. I would say that is likely what accounts for the 4 MB difference.

Check the properties of your hard drive and look for the total of bytes for each drive and then do the math.

 

The total bytes for each hard drive are the same.

 

I think its just basically due to the compressin of the files on each drive, when it copies it won't be literally placed in the same physical places on both hard drives. There will be random spaces between files or even files being fragmented, just run a defrag check on both hard drives (don't defrag them though) and you will probably see the map it comes up with isnt the same for both.

 

All the above posters are missing the mark. If the MB's are different between two drives which are formatted with the same Version of NTFS and identical cluster size, then the contents are not identical.

At least one file is missing on the second drive.

When this happens to my drives; it is usually a small (and usually unneeded) hidden file that is not technically 'data' - but may be needed by some program or even Windows if doing a full system backup/restore from.

As soon as I get this kind of 'indicator' - I am usually replacing/retiring the drive within a month.

But again; make sure that the version of NTFS is identical between all your drives and the cluster size is too.

Any other discrepancy pointed out by the above posters will not affect the 'space used' by identical files on any sized drive.

Good luck.

Forum won't let me edit above post...


Just noticed that you are comparing the size used of folders vs. size used of drives - that is your discrepancy right there (hidden/system folders/files on drive 'root').

 

You're right, I was off the mark, your explanation is a lot more probable.