This allows creating multiple repositories with identical chunker
parameters which is required for working deduplication when copying
snapshots between different repositories.
Use the `Original` field of the copied snapshot to store a persistent
snapshot ID. This can either be the ID of the source snapshot if
`Original` was not yet set or the previous value stored in the
`Original` field. In order to still copy snapshots modified using the
tags command the source snapshot is compared to all snapshots in the
destination repository which have the same persistent ID. Snapshots are
only considered equal if all fields except `Original` and `Parent`
match. That way modified snapshots are still copied while avoiding
duplicate copies at the same time.
Add a copy command to copy snapshots between repositories. It allows the user
to specify a destination repository, password, password-file, password-command
or key-hint to supply the necessary details to open the destination repository.
You need to supply a list of snapshots to copy, snapshots which already exist
in the destination repository will be skipped.
Note, when using the network this becomes rather slow, as it needs to read the
blocks, decrypt them using the source key, then encrypt them again using the
destination key before finally writing them out to the destination repository.
