No abstract

The viability of storage outsourcing is critically dependent on the access performance of remote storage. We study this issue by measuring the behavior of a broad variety of I/O-intensive benchmarks as they access remote storage over an IP network. We measure the effect of network latencies that correspond to distances ranging from a local neighborhood to halfway across a continent.We then measure the effect of latency-hiding mechanisms. Our results indicate that, in many cases, the adverse effects of network delay can be rendered inconsequential by clever file system and operating system techniques.

We sugg=t a practical and economical way to generate random bits using a computer disk drive * a source of randomn-.It requirw no additiond hardware (given a system with a disk), and no user involvement. As a concrete example of performance, on a Sun Wtra-1 with a Seagate Cheetah disk, it generatw bits at a rate of either 5 bits per minute or 577 bits per minute depending on the physical phenomena that we use = a source of randomness. The generated bits are random by a theoretical argument, and *O pass a severe battery of statiaticrd twts.

No abstract

In modern I/O architectures, multiple disk drives are attach e d t o e a c h I/O controller. A study of the performance of such a r c hitectures under I/O-intensive w orkloads has revealed a performance impairment that results from a p r eviously unknown form of convoy behavior in disk I/O. In this paper, we describe measurements of the read performance of multiple disks that share a SCSI bus under a heavy workload, and develop and validate formulas that accurately characterize the observed performance (to within 12% on several platforms for I/O sizes in the range 16{128 KB). Two terms in the formula clearly characterize the lost performance seen in our experiments. We describe techniques to deal with the performance impairment, via user-level workarounds that achieve greater overlap of bus transfers with disk seeks, and that increase the percentage of transfers that occur at the full bus bandwidth rather than at the lower bandwidth of a disk head. Experiments show bandwidth improvements of 10{20% when using these user-level techniques, but only in the case of large I/Os.