How to archive a 30 GB file

I'd recommend against archiving to DVDs since they're inconvenient for large projects and just as susceptible to bit rot as hard drives. If you MUST archive to optical, you should use M-Discs (requires special hardware) or 100-year discs, not standard writeable DVDs off the shelf.

My preference is an archival filesystem (naturally, since I helped develop one).

I'm a filmmaker and editor with lots of footage and project files that I used to keep on hard drives in anti-static bags on a shelf. Not ideal since eventually hard drives will bit-rot. For the last couple of years I've been moving finished projects and footage off my Macs onto a PC running MagnaStor and replicating to Amazon S3 buckets in Ireland, California and Singapore.

MagnaStor is a filesystem (e.g. NTFS) that you put on any hard drive (internal, external, USB stick, doesn't matter) that constantly monitors the data on it and self-heals. I worked on a documentary in the UK in 2004-2005 and the footage we shot was VERY precious to me. I like knowing now that not only is my data co-located all around the globe, but that the data I have on my office fileserver is constantly watched over and healed so that if I ever need it in the future it'll be there. A single 2TB drive currently hosts all the stuff I want archived and getting at it is as easy as copying it.

Full disclosure: I am one of the developers on the MagnaStor archival filesystem, but also a user who has definitely benefitted from it.

You can download it at http://magnastor.com/

7-Zip can do this:

1. If not already done, would recommend setting the file editor to something better than the Windows standard Notepad, e.g. Notepad++. To do this in 7-Zip, go to Tools -> Options..., select the editor tab and change the "Editor" path (and may as well also change the "View" path) to the relevant executable, e.g. "C:\Program Files (x86)\Notepad++\notepad++.exe" -multiInst. The -multiInst option opens this in a new window - see comment from Simo Kivistö.
2. Open the archive in 7-Zip.
3. Locate the file to be edited.
4. Right-click on the file to edit and select "Edit" (alternative shortcut = F4). Make your changes, save them and close the editor window - 7-Zip will only detect the file has changed when the editor has been closed.
5. When 7-Zip detects the file has been changed it will display a prompt such as "File 'abc.txt' was modified. Do you want to update it in the archive?". Click on OK and it will then load the changed file back into the zip file, which may take a bit of time.