Is it possible to download TeX Live in a separate, single file?

If you want to have a "resume/pause"- like feature when downloading TeXLive then mirroring it on your hard drive is a good approach.

Advantages of mirroring TeXLive:

1. We can pause or resume the download.
2. We can share the raw TeX distribution for other users in our local network. As a result, we save internet bandwidth.
3. We can update or sync our single raw TeX mirror with a public nearest mirror on the internet. The installed TeX systems on the local network then update from our local mirror. It saves internet bandwidth. Updating or syncing our local mirror with a public mirror runs fast because a smart algorithm has been adopted in a sync tool that will be used and explained below.

How to mirror:

I assume that your OS is Windows. Otherwise, you need to search for similar procedures.

1. First download cwrsync version 5.5 from itefix.net (the download link is in the "free" tab). Unpack it to C:\Program Files (x86)\ and add C:\Program Files (x86)\cwrsync_5.5.0_x86_free\bin to your system variable PATH.

2. Fix the file permission issue by doing the procedures explained in this link.

3. Locate the nearest TeXLive mirror, and execute the following from cmd.

   rsync -a --delete -v --progress rsync://<your nearest mirror>/CTAN/systems/texlive/tlnet/ "/cygdrive/<your drive name>/<your destination folder>"
   

For example,

rsync -a --delete -v --progress rsync://ftp.fau.de/ctan/systems/texlive/tlnet/ "/cygdrive/d/Installers/TeXLive2020"

For more detailed, please visit Downloading/mirroring the TeX Live repository

Tips and Trick:

Typing

rsync -a --delete -v --progress rsync://<your nearest mirror>/CTAN/systems/texlive/tlnet/ "/cygdrive/<your drive name>/<your destination folder>"

seems to be cumbersome for us. Therefore, I suggest you to create a batch file as follows

rem this filename is UpdateMyTeXLive.bat

rem the file path must not contain spaces
rem trailing / at the destionation is optional


rsync -a --delete -v --progress rsync://<your nearest mirror>/CTAN/systems/texlive/tlnet/ "/cygdrive/<your drive name>/<your destination folder>"

and name it something like

Whenever you want to update your local TeX mirror, just right click the icon and choose "Run as administrator".

Updating the installed TeX system:

Updating your local TeXLive mirror has nothing to do with updating your installed TeXLive.

If you have installed TeXLive on your machine and you have just updated your local TeX mirror, then the installed TeXLive on your machine must be updated or synced with your local TeX mirror. To update your installed TeXLive see this answer.

I suggest to download one ISO file from a mirror of your choice or via Torrent. You can find some links here.

I think, now more than ever, that this is the most advantagious way to acquire TeXLive because the 2012 version has been released few days ago, so the DVD is really up-to-date at the moment and, with torrent or with a good mirror, you'll have it in two or three hours (with a good internet connection). 2.2 GiB is not a big deal nowadays