ADAPTIVE BLOCK REARRANGEMENT

An adaptive technique for reducing disk seek times is described. The t echnique copies frequently referenced blocks from their original locat ions to reserved space near the middle of the disk. Reference frequenc ies need not be known in advance. Instead, they are estimated by monit oring the stream of arriving requests. Trace-driven simulations show t hat seek times can be cut substantially by copying only a small number of blocks using this technique. The technique has been implemented by modifying a UNIX device driver. No modifications are required to the file system that uses the driver.