Solved Two identical HDD. Backed up one of them but space differs

January 4, 2018 at 23:31:53
Specs: Windows 10
I’ve transferred all data (3.15TB) on disc ‘A’ to disc ‘B’ using TetraCopy. Both drives formatted to NTFS. When the transfer completed, some 14 hours later, the target disc ‘B’ had approximately 985MB less data than disc ‘A’. However, all files on disc ‘B’ were complete with no errors. Which is good, but why the huge discrepancy between the two? Both drives recycle bins were empty. I checked drive ‘A’ before starting the transfer and again after.

I have now performed the same transfer three times, formatting drive ‘B’ to NTFS each time.

I use these drives for video, music & photos via a separate media player. I use drive ‘A’ as a backup and was intending to use ‘B’ with the media player, but even though both of these drives have carbon copies of the media, ONLY drive ‘A’ is recognised by the player, this is the one with 985MB more data on it.

The drives are a pair of 5TB WD Elements which in the real world give me 4.54TB on each.


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January 5, 2018 at 00:58:06
✔ Best Answer
Maybe cloning the drives can do the trick?

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January 5, 2018 at 01:57:59
Thanks for the suggestion, I'll give it a try over the weekend. I forgot to mention that I also tried SyncToy & another sync programme named Free File Sync.

message edited by Scratcher

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January 5, 2018 at 04:47:25
Hi Scratcher,

why worry?

The amount involved is small and could be due to files being better placed on the target hdd,, instead of in the same positions as the source. This would reduce indexing information.

You could try defragging the source, but this may not cure the problem 100% as it is not the same as writing to a virgin hdd.

Good Luck - Keep us posted.

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Related Solutions

January 5, 2018 at 05:24:47
What make/model is the "media player"?

How was Disk A derived; as in where is it normally housed and how was "its" content recorded?

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January 5, 2018 at 12:52:29
If you only copied 'C' drive then you did not copy over the entire drive which includes the boot partition and a system reserve partition. If you are trying to use one as a swap out instead of the other then you have to use the Clone feature and select the entire drive, not just the single partition.

You have to be a little bit crazy to keep you from going insane.

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January 5, 2018 at 14:10:51
Excellent point by Fingers in #5...

Cloning the drive would bring over the required boot data etc. which a simple copy wouldn't.

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January 9, 2018 at 19:33:38
In the first instance I would like to apologies to all for the delay in providing an update.

Now, it appears that making a clone of drive ‘A’ did the trick as my media player, a Mede8er, now recognises my drive ‘B’. However, I still don’t understand that just syncing drives ‘A’ & ‘B’ instead of cloning wasn’t sufficient in itself. After all, neither drives had any programmes on them; they were purely for the storage & playback of videos, music & photos.

If anyone can explain why syncing didn’t work, then I’m all ears. Please remember that neither of the drives was a ‘C’ drive.

I’ve chosen ‘sluc’ as the Best Answer as he/she was first to suggest cloning.


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January 9, 2018 at 20:45:42
Syncing copied the files only leaving the locations and other details about the files on the other drive. Cloning the drive copied over everything on the drive including file allocation tables, any hidden files that media player uses for itself and identifying things, etc.
"I’ve chosen ‘sluc’ as the Best Answer as he/she was first to suggest cloning." - as you should have.
I was attempting to explain the reasons and agree, I did miss that it was not the C drive so my explanation was slightly off. The new explanation may not be completely technically correct or at least complete but it is to help your understanding of the difference between copying files and copying/cloning an entire drive (or even a partition).

You have to be a little bit crazy to keep you from going insane.

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January 9, 2018 at 22:21:04
Thank you Fingers for your explanation. I hope I've fully understood you but I do have trouble grasping things due to a head injury.

Now, what about the following scenario? I have disc 'A' as my backup and from time to time I'll need to add files to that drive as my media library will inevitably grow. At the time I copy new files to drive ‘A’, I will also need to disconnect drive 'B' from my media player, and copy the same files to that.

So are you suggesting that because I only copied the new files across from drive ‘A’ to drive ‘B’ instead of performing another clone, that the new files on drive ‘B’ won’t be recognised by my media player? I don’t fancy having to perform a clone each time I add new files. The clone I just performed took a shade over 20 hours!

Sorry if I’ve got this all wrong.

Thanks once again.

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January 10, 2018 at 02:20:38
A drive that is a clone (in your case B is a clone of A) is to all extents treatable as if the original. So just as you can simply add files to the original A drive, you can add them to the clone version B.

i.e. either "copy" them from A to B (which is a clone o A) or simply add them to B as you added them to A. Either way the end result is the same.

It doesn't matter which drive has the updates (new data added) first. Once the two drives are the same, one being a clone of the other (in your case B is clone of A), they are interchangable...

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January 10, 2018 at 14:43:33
Eureka! Finally I’ve got it.

Thank you to one and all for your help & patience.


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