Update deduplication.md

src/commands/misc/deduplication.md

@@ -1,20 +1,28 @@
 # Ensuring deduplication for copied snapshots
 
-Even though the copy command can transfer snapshots between arbitrary
-repositories, deduplication between snapshots from the source and destination
-repository may not work. To ensure proper deduplication, both repositories have
-to use the same parameters for splitting large files into smaller chunks, which
-requires additional setup steps. With the same parameters rustic will for both
-repositories split identical files into identical chunks and therefore
-deduplication also works for snapshots copied between these repositories.
+Different repositories usually have different parameters for splitting larger
+files into smaller chunks. When copying snapshots between arbitrary repository,
+deduplication between snapshots from the source and destination repository
+doesn't work unless the repositories share the same parameters, the so-called
+chunker parameters.
 
-The chunker parameters are generated once when creating a new (destination)
-repository. That is for a copy destination repository we have to instruct rustic
-to initialize it using the same chunker parameters as the source repository:
+Rustic enforces identical chunker parameters - if you try to copy to a
+repository with different chunker parameter, you get an error like
 
 ```console
-rustic -r /srv/rustic-repo-copy init --repo2 /srv/rustic-repo --copy-chunker-params
+cannot copy to repository with different chunker parameter (re-chunking not implemented)!
 ```
 
-Note that it is not possible to change the chunker parameters of an existing
-repository.
+Note: Currently it is not possible to change the chunker parameters of existing
+repositories (re-chunking is not yet implemented).
+
+To create a repository with identical chunker parameters to a source repository,
+don't initialize the target repository, but instead run the first `copy` command
+with the `--init` option. This option initializes non-existing repositories with
+the correct chunker parameter:
+
+```console
+rustic copy --init [SNAPSHOTS]
+```
+
+Note: The target repositories must be defined in the config file.