Looking over some E-Series documentation...
The seven-segment LEDs display the shelf ID, and 99 is the normal ID for controller-drive shelves. Expansion-drive shelves display numbers starting with 00 and increasing as drive shelves are added to the storage system. These shelf IDs can be changed from the default numbering by using the SANtricity management interface. The seven-segment LEDs also display status codes under start-up conditions and some error conditions.