On the backup program used, if direct copy or verification of copy is also involved, speed of computer and the backup device (which may be limited to USB1 or 2 speeds, or over a wired LAN or wireless). I don't think anyone can say conclusively. I'd expect it to last about as long as doing a full Defrag on a drive, and I've known those to take all night. When I used to have Windows, running Defrag would be set at bedtime and by morning it usually was done, sometimes not completely.
How long should a 1.6 TB Full backup take on a server with Windows Server 2012 and 32 GB of memory (RAM)? Is 6.5 hours too long or average?

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