Copy pasting from Desktop folder to external HDD increases file size

I was constantly doing backup every day

- why not automate it/ use a backup program - or even a script or schedule Robocopy or Xcopy if it's really simple?
I use Genie Timeline - giveaway available- I just plug in my backup disk and it runs. Simple - and it provides versioned backup and manages the used space if necessary.

did something go wrong with my external Hard drives

You can check of course using e.g. Hard Disk Sentinel (full functional trial/giveaway) or Crystal Diskinfo (free).

folder on desktop is 10GB and when pasting into my 3 external HDDs the file becomes 20GB.

Check you haven't duplicated them or have copies from different dates.
Are you comparing Size or Size on disk in both cases?

You are comparing a folder with a file.. is that what you meant?

A significant difference in cluster size might make the space occupied different if copying many files, but not as much as you're reporting.

To find the ClusterSize (aka BlockSize)
Go to Start
Type CMD
Select "Run as Administrator"

Enter and run command:
wmic volume get driveletter,blocksize

For example for my computer:

Code:

C:\Windows\system32>wmic volume get driveletter,blocksize
BlockSize  DriveLetter
4096       C:
4096
4096       D:
2097152    E:
4096       F:
1024
           M:

That means

C: ADATA SX8200PNP (2TB M.2 NVME SSD)
Format Type: NTFS
Cluster Size : 4096 bytes

D: INTEL SSDPEKNW020T8 (2TB M.2 NVME SSD)
Format Type: NTFS
Cluster Size : 4096 bytes

E: WD My Book (6TB USB/SATA HDD)
Format Type: exFAT
Cluster Size : 2,097,152 bytes

F: WD Elements (12TB USB/SATA HDD)
Format Type: NTFS
Cluster Size : 4096 bytes

I created a small text file with size 1024 bytes on C:. I then copied it to E:. Here are the properties on each:



I copied a large ISO file with size 5.17 GB on C:. I then copied it to E:. Here are the properties on each:



As you can see the files on the disk with the larger cluster size take up more space but not twice as much. That shows a larger cluster size does not explain the large 10GB file being twice as large on the other disk.

It can be that the C: drive is compacted and the external drive isn't.
That will explain why a 10GB when pasting into the 3 external HDDs the file becomes 20GB

- and following that idea maybe NTFS compression is in use on the source folder. However, if they are image files, compression may no be a factor.