We examine the development of mesoscale structure during 3-D magnetic reconnection which initiates from random perturbations. Reconnection develops as multiple x-line segments with characteristic scale lengths of ~1--4 Re in the cross tail direction. For relatively wide initial current sheets (several c/ωpi), these finite length x-lines remain spatially isolated and drive reconnection which is strongly reminiscent of bursty bulk flows (BBFs) in the magnetotail. In narrower initial current layers the x-line segments merge together to a state in which large scale magnetic energy release takes place. Thus, the degree of compression of the magnetotail may ultimately determine if energy is released in local bursts or globally as a substorm.