Data storage device providing communication between processing units

A method for storing, and maintaining and tracking synchronism between, multiple copies of identifiable data volumes in a plurality of data storage devices, for use by at least one host and transparent to said hosts, said hosts addressing commands relating to said identifiable data volumes using access addresses, said hosts supplying said identifiable data volumes to be stored, and receiving said identifiable data volumes, said identifiable data volumes stored on accessed rewritable data storage media accessible in said plurality of data storage devices, said directors respectively unconnected to each other, said directors each separately coupled to said plurality of separate data storage devices, said data storage devices respectively unconnected to each other, said data storage devices each having a buffer, said method comprising the steps of:

• receiving, in said plurality of directors, commands relating to said identifiable data volumes;
• responding, in each of said plurality of directors, to ones of separately partitioned access addresses addressed by said at least one host, and to any accompanying data volume supplied by said addressing host;
• said responding director in turn supplying said command and accompanying data volume to all of said plurality of data storage devices;
• providing, in each said data storage device, a synchronization token to be directly associated with each said data volume, said synchronization token comprising an updatable token;
• said responding director comparing the current value of each said synchronization token directly associated with said supplied data volume for each said data storage device, identifying any of said compared synchronization tokens as down level from the most current token;
• upon said comparing step identifying any of said down level synchronization tokens, said responding director notifying the other of said plurality of directors of the value of said most current token for said data volume, said notifying step comprising:
• receiving, at at least one of said plurality of separate data storage devices, a “broadcast” command from one of said directors, said command accompanied by a message notifying said directors of said most current token value for said data volume;
• storing, at said at least one of said plurality of data storage devices, said received accompanying message in said buffer;
• forwarding, from said at least one of said plurality of data storage devices, a “message ready” signal to at least one of said directors;
• receiving, at said at least one of said plurality of data storage devices, “read message” commands sent from said at least one director;
• and
• supplying, in response to each said received “read message” command, said message stored in said buffer to said sending director, notifying said sending director of said current token value for said data volume;
• and
• said responding director asynchronously updating said provided synchronization token directly associated with said supplied data volume for each said data storage device to said most current token value.