Try to allow the initialization to complete first before tests. Also what was the system status from CPU readings.
When systems saw performance issues was the GUI of the DSS slow or not. Many times overhead or bottlenecks could be some other area. Send in the logs to engineering to verify speeds of drives are other cause. iSCSI and FC Volumes are given the choice to use the Initialization.

Notes from manual:

This option is available when creating iSCSI volume(s), its for security reasons. iSCSI volume will be initialized after creation process. When iSCSI volume is initializing then 'enque' button will show up. With this button you can send iSCSI volume that is initializing to the back of the initialization queue. Every volume that is waiting in queue for initialization can be also send to the back of queue, the same as volume that is already initializing.