Phantom files for dynamic read bandwidth measurements of computer disks

Abstract

An improved method for supporting an empirical measurement of the data bandwidth that one or more computer disks can continuously sustain while reading data. In a computer system having predetermined workload requirements and disk storage for storing an allocation table including entries for meta blocks and data blocks, a method for supporting a dynamic measurement of the read bandwidth of a disk, includes the steps of: creating an alternate allocation table that ignores the existing content of the disk; creating meta blocks for a phantom file by allocating the meta blocks from the allocation table; allocating data blocks for the phantom file from the alternate allocation table; and writing only meta blocks to the disk, but not actual data blocks. Since the actual data blocks are by far the largest component of the files, phantom files require only a very small number of disk blocks, and can be written very quickly. Since the creation of the alternate allocation table ignores the existing content of the disk, disks can be used regardless of their current content and without modifying this content. Further, a disk can be calibrated by reading phantom files--using all system components including hardware and software--in the same way that the application for which the calibration is intended would read ordinary files thereby avoiding any artifacts resulting from the measurement of the read bandwidth.