Reducing Disk Rotation Delays using Range Writes

Disk I/O is generally considered the bottleneck in memory operations. This is generally due to mechanical limitations (limited disk rotation caps transfer bandwidth), and the general architecture of modern disks (rotating platters accessed by a single head on the arm), which causes a delay on the positioning of the head. Operating systems are generally able to fight the seek delays by writing to blocks not far away from each other, but tackling the rotational delay problem is much more complicated. We propose a method to fight the disk rotational delays, dubbed Range Writes, by allowing for the operating system to give a wider flexibility to disk to perform a write, potentially saving significant rotational delays. Instead of providing just one logical block, in Range Writes the file system can provide multiple blocks for disk to write data to, thus allowing the disk to make a smart decision and save some rotational delay. We provide an implementation of Range Writes on Disksim disk simulator, and show the savings in rotational delays and total positioning time. Our experiments show up to 32% improvement in rotational delays for write-intensive work-