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?