Various embodiments (“systems”) are described for transferring data from a primary storage (e.g., magnetic disk drives, solid state drives, etc.) to an optical cold storage rack. The optical cold storage rack may include many physical optical storage disks, but a much smaller number of burners and readers (e.g., optical disk drives). When data is to be transferred to the optical cold storage rack, the system may generate a plan for performing the transfer. “Migration worker” components may then implement the plan and may be exclusively dedicated to implementing such plans. In various embodiments, the plan may specify how large data file “aggregates” (collections of portions of one or more data files) are to be distributed across optical disks (“disks”) to improve throughput during subsequent reading operations from the optical cold storage rack. The plan may also anticipate the relation between the limited number of burners/readers and the overall optical cold storage rack disk capacity.