Continuous recording multichannel disk-based data logging apparatus. The apparatus includes a plurality of disk drives and an interface including a plurality of parallel inputs. The interface is responsive to data at the inputs to write the data on an active plurality of the disk drives, at least one disk drive being idle. The interface is responsive to a user request for data on one of the active disk drives to substitute an idle disk drive into the active plurality in place of that one, to read the requested data, and to cause that one to become idle.