Can't copy system image - Not enough space

I have a system image folder (WindowsImageBackup) of windows 8.1 on an external hdd. The size of the folder and sub folders is a total of 42GB. I tried to copy this folder to another external hdd that has only one partition, with 45GB free. When I try to copy the image folder, I get a message saying that there is not enough space on the target drive. It says I need an additional 39GB on the target drive to copy these files. So, the error message is telling me that I need 81GB of free space on the target drive to copy 42GB of files to it. The message correctly states the free space available on the target drive is 45GB. Why would the target drive need nearly twice the free space of the files being copied to it?

I have no idea why it's giving you that message but try coping it with TeraCopy. I have read it creates a hash before the copy begins and checks the hash on the files that were copied. They have a free version and a paid. I use the free.

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At least one backup program that I've used for years, does not like to have its Backup Image Files moved. For some undocumented reason, if you move a backup Image File, it won't work any more.

Is there anything keeping you from simply making a new Backup Image and putting it where you want it to be (permanently).

Rarely, have I ever had a situation, where I could only save one backup image file to a particular location. But when I did, I would simply delete the old Image file before creating a new one.

It looks like your Backup Image file is awfully BIG! Unless, you're saving an awful lot of pictures or videos to your C: drive.

Something I always do, before backing up my C: drive, is to give it a very thorough cleaning. I first remove every file that is not required to be there. I even clean and defrag my registry, to make it as small as possible.

Then when I run my backup program from a boot disk, I have the ability to delete all the old Restore Points, Pagefile, and Swapfile. That prevents all those BIG files from being added to my Backup Image File. I also use FAST Compression of the Backup Image.
So the result is that my Backup Image is much smaller than the size of my normal C: partition.
If your backup program can't do that, then you should use a different backup program.

So rather than trying to move your backup file to a new location, why not just make a new backup file, to that location?

Good Luck,
TechnoMage

Thanks to all for all the good tips. I wound up just making a new image. I first tried some copying using SyncBack which I use for regular data backups, and it worked fine the first time, but then on subsequent copies I was getting I/O errors on two different drives. I don't think the drives are bad; they pass all the tests I run on them. The I/O errors were reported by SyncBack to involve the 43GB .vhdx image file. One of the target drives got all messed up, apparently from the failed attempt by SyncBack to copy the files. Chkdsk /f finally fixed the files on the drive.

I still have no idea why Windows Explorer told me I need twice the space that the image files take up, but for now, saving a new image was the quickest way to get it to another location.