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?
WellingtonISAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

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?
0
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.
0
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.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Big Business Goals? Which KPIs Will Help You

The most successful MSPs rely on metrics – known as key performance indicators (KPIs) – for making informed decisions that help their businesses thrive, rather than just survive. This eBook provides an overview of the most important KPIs used by top MSPs.

WellingtonISAuthor Commented:
Thanks at least I' m safe
0
JohnBusiness Consultant (Owner)Commented:
I think so, yes
0
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.
0
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...
0
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

Open in new window


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

Open in new window


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
1
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Storage

From novice to tech pro — start learning today.