To put beyond loss. Both rescuing a thing and committing it to keeping.
Latin salvare (to make safe, preserve), from salvus (safe) — the same root that gives safe; the sense of committing a file to keeping descends directly from the older sense of rescuing a thing from loss.
To put a thing beyond loss — the rescuing sense and the committing-to-keeping sense are, by the word's own history, the same act twice.