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Size vs Size on Disk

I have a corrupt drive according to windows.  This is a san and there nothing wrong with the drive. This is a darn windows issue.  Nevertheless, I have the information backed up on a NAS and because this information is vital, I'm checking the sizes of each folder just to be sure.  I'm a bit confused because on the live drive I'm getting the following information:
example:
Live Drive                                                     Back up San
2004 size 435/size on disk 449                 size 435/size on disk 438
2005 size 500/size on disk 510                 size 500/size on disk 502
2006 size 527/size on disk 539                 size 527/size on did 529

I've already lost 3 days of this vital data due to disk corruption and I don't want that to happen again.  Am I ok?
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WellingtonIS
Asked:
WellingtonIS
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3 Solutions
 
JohnBusiness Consultant (Owner)Commented:
Size on disk is always a bit different than the logical size. That is normal in the Windows File system.

So I think you are OK. Can you keep a backup before proceeding?
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WellingtonISAuthor Commented:
well so far the sizes match.  I think I'm going to robocopy what's on the live "corrupt" disk just to be sure.
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oBdACommented:
The "size on disk" depends on the cluster size used when formatting the disk. You can safely disregard any differences there.
This is the size that remains unused in the last cluster allocated for the file.
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WellingtonISAuthor Commented:
Thanks at least I' m safe
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JohnBusiness Consultant (Owner)Commented:
I think so, yes
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oBdACommented:
"This is the size that remains unused in the last cluster allocated for the file." should of course have been "The difference is the size that remains unused in the last cluster allocated for the file." You may have noticed that the "size on disk" is always larger than the actual size.
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nociSoftware EngineerCommented:
Does the content compare equal?.... sizes say nothing about content of files.
The file might have been allocated and still be full of zero's because data wasn't written to it...
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oBdACommented:
If you need to be absolutely sure, you can run a hash comparison (the download below contains just a stand-alone exe that can just be copied to wherever you need it).
First create a checksum file for the "live" folder (maybe try it with a smaller test folder first to get a feel for it).
-add creates/adds a checksum database
-r is Recurse.
-bp sets the BasePath, which will be removed when storing the hash (required because you want to compare two different folders).
-xml sets the file where the hashes will be stored. Note: when this file exists (for example from a previous run against a different folder), the entries will be added to the existing ones, it will not be overwritten!
fciv.exe -add D:\Live\Data -r -bp D:\Live\Data -xml C:\Temp\fciv.xml

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Now verify against the backup.
-v is Verify
The first folder must be the one in backup that matches the one where the respective files from the first run are stored.
-bp sets the BasePath again, must be the same as the first folder in this command.
-xml sets the file with the hashes from the first run
> redirects the output to the file specified
fciv.exe -v E:\Backup\Data -r -bp E:\Backup\Data -xml C:\Temp\fciv.xml >C:\Temp\fciv_results.txt

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Availability and description of the File Checksum Integrity Verifier utility
https://support.microsoft.com/en-us/help/841290/availability-and-description-of-the-file-checksum-integrity-verifier-u
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