how to Re-install FF XIV with out reloading patch

I have to format my PC and re-install windows (some virus problem.)
I want to back up FFXIV patch before formatting HDD due to it gonna take a long time to loading patch if I install FFXIV from original DVD game.

Do you have any suggestion?

You just need the folder where you installed ffxiv and maybe the ffxiv in username\My Documents\My Games\ if you want to keep your settings.
You get those on the new installation and just start the config again. Sadly there's no way to backup just the patch as it gets deleted right after it got applied.

Well, I backed up the entire SQUAREENIX folder on a different drive.

Then reinstalled the game, then copy the game from the backed up folder overwriting everything that is fresh installed.

You'll get an error on the patcher once you run it the first time, you just have to rerun it the second time and it'll be working.

** I'm not sure if it has any side effects though.

Nah I did the same and it still works :P
Maybe make sure that there's no write-protected file before installing the next patch(otherwise it can break the installation).