etcd is designed to handle small key value pairs typical for metadata. Larger requests will work, but may increase the latency of other requests. By default, the maximum size of any request is 1.5 MiB. This limit is configurable through --max-request-bytes flag for etcd server.
The default storage size limit is 2GB, configurable with --quota-backend-bytes flag. 8GB is a suggested maximum size for normal environments and etcd warns at startup if the configured value exceeds it.