Apparatus and method for controlling data flow between a computer and memory devices

An apparatus for linking a computer to a plurality of memory devices, comprising:

• at least first and second first-level data routing controller means for handling input/output storage communications with the computer;
• first and second buses coupling said first and second data routing controller means, respectively, to said computer;
• at least first and second second-level data routing controller means, each connected to each of said first-level data routing controller means and each other, for routing data from said first-level data routing controller means to first and second groups of said memory devices, respectively;
• switching means, coupled between said first and second second-level data routing controller means and said first and second groups of memory devices, for coupling said first and second groups of memory devices to said first second-level data routing controller means in response to first and second activate signals, respectively, from said first second-level data routing controller means, and for coupling said first and second groups of memory devices to said second second-level data routing controller means in response to second and first activate signals, respectively, from said second second-level data routing controller means;
• and
• each of said second-level data routing controller means, in the absence of a failure, providing said first activating signal to couple to only one of said groups of memory devices and including controller recovery system means for, responsive to a failure in the other second-level data routing controller means, providing said second activating signal to said switching means to couple to both of said groups of memory devices.