| `bucket` | yes | The name of your Google Cloud Storage bucket where you wish to store objects (needs to already be created prior to driver initialization). |
| `keyfile` | no | A private service account key file in JSON format used for [Service Account Authentication](https://cloud.google.com/storage/docs/authentication#service_accounts). |
| `rootdirectory` | no | The root directory tree in which all registry files are stored. Defaults to the empty string (bucket root). If a prefix is used, the path `bucketname/<prefix>` has to be pre-created before starting the registry. The prefix is applied to all Google Cloud Storage keys to allow you to segment data in your bucket if necessary.|
| `chunksize` | no (default 5242880) | This is the chunk size used for uploading large blobs, must be a multiple of 256*1024. |
**Note:** Instead of a key file you can use [Google Application Default Credentials](https://developers.google.com/identity/protocols/application-default-credentials).
