> Do I use `rsync --append` for all invocations?

Yes, you would use it each time (the first time there is nothing to append, so it's a no-op; the second and subsequent times it's actioned). But **do not use `--append` at all** unless you can **guarantee** that the **source is unchanged** from the previous run (if any), because it turns off the checking of what has previously been copied.

> Does `rsync --append` resume for the subsequent invocations… without reading all the already copied data?

Yes, but without `rsync --partial` would probably have first deleted the target file.

The correct invocation would be something like this:

 rsync -a -vi --append --inplace --partial --progress /path/to/source/ /path/to/target

You could remove `--progress` if you didn't want to see a progress indicator, and `-vi` if you are less bothered about a more informational result (you'll still get told if it succeeds or fails). You may see `-P` used in other situations: this is the same as `--partial --progress` and can be used for that here too.

- `--append` to continue after a restart without checking previously transferred data
- `--partial` to keep partially transferred files
- `--inplace` to force the update to be in-place

If you are in any doubt at all that the source might have changed since the first attempt at `rsync`, use the (much) slower `--append-verify` instead of `--append`.