How do I specify multiple filesystem back ends for glance image store?

Issue

• When we use the option "filesystem_store_datadir=/var/lib/glance/images301/" in the glance-api.conf file, glance starts without any problems.
• But when we try to setup multiple datadirs with multiple lines of the option "filesystem_store_datadirs=" we get the following error:

Failed to configure store correctly: Store filesystem could not be configured correctly. Reason: Specify either 'filesystem_store_datadir' or 'filesystem_store_datadirs' option Disabling add method.

• We made sure the first option was commented, as specified in the error message. How can we correctly configure multiple filesystem backends for glance?