Disaggregated data storage and retrieval system

A data-storage system comprising:

• a head receiver configured to variably receive up to a number M of write heads;
• an installed number N of write heads arranged in the head receiver, wherein each of the installed number N of write heads is configured to encode data as a localized birefringence in an associated data-storage substrate or to encode data in holographic data storage;
• a substrate receiver configured to receive one or more data-storage substrates;
• and
• a positioner machine configured to adjust a relative placement of each of the M write heads with respect to at least one of the one or more data-storage substrates.