GCS Metadata Path (Optional)
In case of minimal downtime sharded migration, for each shard, the Datastream jobs launched by the Spanner Migration Tool write data to a destination path on Google Cloud Storage. To store the metadata information such as session file, a new GCS Bucket is hence created. If the user does not wish for a new GCS Bucket to be created or wishes to name the bucket created, then the GCS Metadata Path Parameter can be set optionally.