I have a local repository with more history than my remote B2 repository, so I’d like to upload some snapshots from the local repo to the remote (and backdate them with --time).
What is the best way to do this? I’m thinking mount the snapshot then backup as a normal source path?
Hi and welcome to the forum 
I think that would be the easiest way to get the data from a single snapshot to a new repository.
If possible it makes sense to use the restic restore --verify to really make sure it’s all good before you move that data to the external repo.
That is one way to do it. Note that fuse doesn’t allow custom inode numbers, so the inode numbers in the new backup will not match the source backup. This shouldn’t matter (the inode numbers are not restored anyway) unless you back up directly to this repository later – restic will be forced to rehash all files as the inode numbers won’t match. This will not affect the validity of the backup but will make it take longer.
Thanks for the info! The local repository is on a FAT32 HDD, and I saw somewhere that FAT32 doesn’t recognise inode numbers anyway? In which case, should I be passing --ignore-inode when backing up locally?
And yeah I do plan to keep backing up directly to the B2 remote repo after I’ve uploaded these backdated snapshots, so should I pass --ignore-inode when uploading the snapshots from the local repo too?
This option could speed up backups, yes. Note that it won’t change the information actually recorded in the repository, it just tells restic that if the inode number has changed, it doesn’t mean that the file contents necessarily changed.