SharePoint 2010 server Farm Backup error

Dear Support,

I am unable to take SharePoint 2013 on-Premise server farm backup using PowerShell command

 Backup-SPFarm -Directory C:\OnpremiseFarmBackUp -BackupMethod full

I am getting following error --

PS C:\Users\spsadministrator> Backup-SPFarm -Directory C:\OnpremiseFarmBackUp -B

ackupMethod full

Backup-SPFarm: There is not enough disk space. Free additional space on your hard disk and then try again. Approximate amount of space needed: 42.77 GB. Amount of space free on disk: 39.26 GB.

At line:1 char:14

+ Backup-SPFarm <<<<  -Directory C:\OnpremiseFarmBackUp -BackupMethod full

    + CategoryInfo         : InvalidData: (Microsoft.Share...mdletBackupFarm:

   SPCmdletBackupFarm) [Backup-SPFarm], SPException

    + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletBackupFarm

Note:- In our organization SharePoint 2013 on premise server farm backup size is only 7 GB and my disk free space is 39.26 GB than why we are facing such type of issue.

Would request you to reply ASAP

Thanks & Regards.

Ajit/Akhilesh