Context: I make backups / archives, primarily of photos. I'm experimenting with Bup, which is designed for backup to hard disk. Basically it creates Git repos which include packfiles of up to 1GB. But I still need last-ditch backups to keep offline and move offsite (and keeping them on read-only media is good too!).

What are the options for archiving and splitting large files over several discs like CDs (and reading them back!)? I'd prefer methods which

• will stay readable in future.
• are portable e.g. to Windows.
• have known simple implementations, so I could re-implement them myself if necessary.

(Using Bup packs will stretch my robustness budget. So I want to be confident about how other parts of the system would behave).

I heard split archives are possible with both ZIP and 7-Zip. Is that right?