Backup Problem, Windows Reserves too Much Space, 800GB?

[webmanoffesto]

I’m using “Windows Backup and Restore” in Windows 7.​

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I'm using SpaceSniffer to evaluate a backup problem.​

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One of my scheduled backups failed. I thought this was because of lack of space. So I opened up SpaceSniffer and saw something surprising:​

C, System Folder, 55.5 GB​

D, Data Folder, 167.5 GB​

I, My 1TB External Drive​

_ 14GB used​

_ 52GB free space​

_ 864GB Unknown (not yet scanned)​

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I thought that the 864GB was “set aside” or used for the backups. But why is it so huge, when “C” and “D” are relatively small? That doesn’t make any sense.​

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What do you recommend I do?​

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SpaceSniffer: http://download.cnet.com/SpaceSniffer/3000-18512_4-10913555.html​

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Earlier problem resolved: A backup of my system files and my data files to my 1TB external drive did not succeed because “Scheduled backup of system images is not allowed on removable devices.”​

 

[biggles1000]

Odd, it should be allowed to backup to external devices. I backup my system all the time to a 500GB external Seagate :/
Is the external drive a standard data holding one or a specialist backup one?