message: [backup] default chunk size: 128M
  So when we do concurrent downloading of chunks to memory, they won't take too much of it.
  It's possible to use more sophisticated streaming and buffering, but this is straightforward.
  Closes:
  Closes:
diff: @@ -25,9 +25,10 @@ use tokio::fs::metadata;
  #[derive(Clone, StructOpt)]
  pub struct GlobalBackupOpt {
  + // Defaults to 128MB, so concurrent chunk downloads won't take up too much memory.
  #[structopt(
  long = "max-chunk-size",
  - default_value = "1073741824",
  + default_value = "134217728",
  help = "Maximum chunk file size in bytes."
  )]
  pub max_chunk_size: usize,
  