add warnings on repository copies to avoid future problem like #4272

[anarcat]

fixes #3933.

[ThomasWaldmann]

well, that is maybe a bit too restrictive.

quite some people e.g. use rclone to have a copy of their local repo in the cloud, just in case their house burns down or so.

[anarcat]

how should i phrase this instead?

[ThomasWaldmann]

we should mention borg with-lock ... here. it will also produce a lock, but it will use the lock so not other borg updates the repo while it is copied / synchronized.

the problem is not making the copy, but using borg to access more than 1 of the set of original and cloned repos (includes: just reading, updating independently, etc.).

[ThomasWaldmann]

@anarcat i improved it myself, have a look.

i chose to refactor it a bit, to make the point more clearer:

• first, talk about what one should do to have multiple redundant repos
• talk less about what one should not do anyway (like copying a repo while a backup is running)
• second, talk about problematic ways to have identical copies of a repo, what the problems are and what one must not do.

[ThomasWaldmann]

also changed "repo2" to "copy-of-repo" to avoid people having the impression that this creates another usable repository.

[ThomasWaldmann]

I'll merge it as is, hopefully it is ok for you @anarcat. Want to get 1.1.9 out tonight.

[anarcat]

thanks for taking this the final steps... :)