According to https://cloud.google.com/appengine/docs/python/datastore/typesandpropertyclasses?hl=en I should use a Blob type but I don't see such type in gcloud-node. Is it something yet to be implemented? How can I save long text in datastore using gcloud-node?
If a property is not indexed, you can store up to 1 MB. (Reference)
See this example for how to disable indexing explicitly.
Have you tried saving data and received an error?