Performance comparison of ide and scsi disks

It is widely believed that the IDE disks found in PCs are inexpensive but slow, whereas the SCSI disks used in servers and workstations are faster, more reliable, and more manageable. The belief that current IDE disks have performance and reliability disadvantages has been called into question by several recent reports. Thus we consider the possibility of achieving tremendous cost advantages by using IDE disks as the foundation of a storage system. In this paper, we give an extensive performance comparison of IDE and SCSI disks. We measure their performance on a variety of micro benchmarks and macro benchmarks, and we explain these results with the help of kernel instrumentation and device activity traces collected by a SCSI analyzer. We consider the impact of several factors, including sequential vs. random workloads, file system enhancements such as journaling and Soft Updates, I/O scheduling in the kernel vs. in the disk drive (as enabled by tagged queuing), and the use of RAID technology to obtain I/O parallelism. In our testbed we find that the IDE disk is faster than the SCSI disk for sequential I/O, but the SCSI disk is faster for random I/O. We also observe that the random I/O performance deficit of the IDE disk is partly overcome by kernel I/O scheduling, and is further mitigated by scheduling in the drive (as enabled by tagged queuing), and by the use of journaling and Soft Updates. Taken as a whole, our results lead us to conclude that RAID systems based on IDE drives can be both faster and significantly less expensive than SCSI RAID systems.