E-Series volumes are not able to be placed online or offline manually. If you create the volume and map it to a host, it is accessible automatically.
Volumes will fail though and become inaccessible in certain situations such as two drives failing in a RAID 5 configuration. Fixing the underlying issue should make the volume accessible again automatically.
You mention that you saw it was possible to online a volume using the CLI. Do you have a link to where you read that?