Whatever happens, never, ever, think that having just copied all of your data on an external hard disk, it is a good time to wipe your main disk clean to selectively import back only recent and important stuff. Or just to achieve drefragmentation, old-skool.
Because the backup disk, even if used for only about an hour, MIGHT FAIL.
And take with it all your digital life: music, pictures, code, documents and the rest.
R.I.P. Maxtor 3200 500GB external drive, 2007 – 2009. Always cursed for speed and noise, only after thou left was your worth acknowledged.