A material handling system comprising: a storage rack having more than one vertically-spaced level, each level having a plurality of storage locations accessible from an adjacent aisle ; a vertical lift having a vertical support structure positioned proximate to the storage rack and having vertically aligned first and second carriages independently positionable along respective first and second vertical portions of the vertical support structure ; a first vertical drive system coupled to the first carriage and configured to position the first carriage to pick up and to deposit articles at selected levels within the first vertical portion of the vertical support structure ; a second vertical drive system coupled to the second carriage and configured to position the second carriage to pick up and to deposit articles at selected levels within the second vertical portion of the vertical support structure ; and a processor subsystem in communication with the first and second vertical drive systems and configured to selectively position the first carriage and the second carriage at respective selective levels without colliding, characterized in that , one or more shuttle vehicles are configured to service respective levels of the storage rack ; and in that each of the first and second vertical drive systems comprises a drive belt received on a front side of the vertical support structure laterally offset and in vertical alignment with each other; the drive belts are received for vertical rotation respectively on passive, coaxial top pulleys and received on independently driven coaxial bottom pulleys ; and first and second drive motors of the first and second vertical drive systems independently rotate the bottom pulleys through a 90° reduction transmission respectively. a storage rack having more than one vertically-spaced level, each level having a plurality of storage locations accessible from an adjacent aisle ; a vertical lift having a vertical support structure positioned proximate to the storage rack and having vertically aligned first and second carriages independently positionable along respective first and second vertical portions of the vertical support structure ; a first vertical drive system coupled to the first carriage and configured to position the first carriage to pick up and to deposit articles at selected levels within the first vertical portion of the vertical support structure ; a second vertical drive system coupled to the second carriage and configured to position the second carriage to pick up and to deposit articles at selected levels within the second vertical portion of the vertical support structure ; and a processor subsystem in communication with the first and second vertical drive systems and configured to selectively position the first carriage and the second carriage at respective selective levels without colliding, characterized in that , one or more shuttle vehicles are configured to service respective levels of the storage rack ; and in that each of the first and second vertical drive systems comprises a drive belt received on a front side of the vertical support structure laterally offset and in vertical alignment with each other; the drive belts are received for vertical rotation respectively on passive, coaxial top pulleys and received on independently driven coaxial bottom pulleys ; and first and second drive motors of the first and second vertical drive systems independently rotate the bottom pulleys through a 90° reduction transmission respectively. <EOS>