You need a downtime or I think you can do a online backup with a agent of Acronis to avoid downtime.
But the size of a physical is not a problem only the downtime frame
You can do a test with a small Linux server so you can see before what changes you must do for your productive system.
And changing fstab was much easier then the backup and restore process
It was the smoothes way I found - no other converter was working.