Queueing models of secondary storage devices

Coffman, E. G.; Hofri, Micha

doi:10.1007/bf01536186

Cited by 20 publications

(5 citation statements)

References 37 publications

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“…With independent uniformly distributed requests the new mean seek distance is 5/36 versus 5/24 [6]. One of the two arms may be dedicated to serving the inner cylinders of the disk and the other arm to the outer cylinders, but even better performance is attainable without this restriction [4]. Even shorter seek times can be achieved if both arms are prepositioned at 1/4 and 3/4, which yields a mean seek distance of 1/8 [8].…”

Section: Performance Studies Of Mirrored Disksmentioning

confidence: 98%

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Mirrored disk rouing and scheduling

Thomasian

2006

Cluster Comput

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Disk mirroring or RAID level 1 stores the same data twice, on two independent disks, to ensure that all single disk failures can be tolerated. This high storage overhead is acceptable in view of the drop in storage cost per gigabyte and rapidly increasing disk capacities. Disk access time, on the other hand, is improving at a very slow pace, so that another important advantage of disk mirroring is the doubling of the disk access bandwidth in processing read requests. Efficient routing of read requests to disks and local disk scheduling can be used to improve performance even further. We are primarily concerned with two RAID1 configurations: (i) source-initiated routing with the independent queues-IQ method; (ii) destination-initiated routing with the shared queue-SQ method. Static, dynamic, and affinity-based (AB) routing methods are used to distribute requests with the IQ method. We compare the performance of various IQ and SQ based routing policies using a random number-driven simulation. While there is some improvement in performance with the more sophisticated routing policies, performance is dominated by the local disk scheduling policy. The SQ method allows resource sharing, so that it tends to outperform the IQ based routing, but it requires the scheduler to keep track of the state of the disk drives. As a further means to improve performance, we consider the effect of prioritizing reads with respect to writes, transposed data allocation, and replicating data more than twice. Mirrored disk schedulingMajor advances in magnetic disk technology have resulted in very high areal recording densities. There has been a three order of magnitude increase in disk capacities in the last decade and a dramatic drop in the per gigabyte cost. Due to the increased linear recording density, the transfer time of small blocks of data accessed by online transaction processing-OLTP applications constitutes a small fraction of disk rotation time, so it is negligibly small compared to disk positioning time, i.e., the sum of seek time and rotational latency. The increase in disk RPMs also contributes to this effect, but more importantly to reducing the rotational latency, which for small block transfers is roughly one half of disk rotation time. The improvement in seek time is also very slow due to its mechanical nature. The overall reduction in disk positioning time is below 8% annually [5].The fact that the improvement in disk access time lags far behind the increase in disk capacities is especially important for OLTP applications, which are concerned with random accesses to small data blocks. The performance of certain benchmarks specified by the Transaction Processing Council 1 is determined by the maximum throughput, while transaction response time is below a certain threshold. Transaction response time is affected by the number of disk accesses, which are carried out on its behalf. The database buffer in main memory is effective in eliminating a 1 http://www.tpc.org.Springer

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Section: Performance Studies Of Mirrored Disksmentioning

confidence: 98%

“…This is because analytic solutions for disk scheduling and load sharing and balancing are rather limited, see [4] and [33], respectively. We consider a random-number-driven simulation, since it is more flexible than trace-driven simulation, e.g., the difficulty of varying the arrival rate of requests.…”

Section: Simulation Modelmentioning

confidence: 99%

Mirrored disk rouing and scheduling

Thomasian

2006

Cluster Comput

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“…• If there is a Write batch and Diskj is not processing a Write batch, Diski will start processing the Write batch even though the Read queue is non-empty. 4. Completion of a Write at Diski.…”

Section: Bwi-number Of Write Requests Left In the Batch Being Processmentioning

confidence: 98%

“…The use of simulation is necessitated, because analytic solutions for realistic disk models and queueing disciplines have only been developed for the FCFS policy with Poisson arrivals, the so-called M/G/1 queueing model [7]. A more complex analysis required for zoned disks is reported in [18,24], Analytic solutions for other disk scheduling policies are rather limited [4].…”

Section: Simulation Modelmentioning

confidence: 99%

Performance Comparison of Mirrored Disk Scheduling Methods with a Shared Non-Volatile Cache

Thomasian

Liu

2005

Distrib Parallel Databases

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Mirrored disks or RAID1 is a popular disk array paradigm, which in addition to fault-tolerance, doubles the data access bandwidth. This is important in view of rapidly increasing disk capacities and the slow improvement in disk access time. Caching of dirty data blocks in a non-volatile storage (NVS) cache allows the destaging of dirty blocks to be deferrable, so as to improve the response time of read requests by giving them a higher priority than write requests. Destaging of dirty blocks in batches to take advantage of disk geometry entails in lowered disk utilization due to writes and improved performance for reads. Polyzois et al. [12] propose a scheduling policy for mirrored disks equipped with an NVS cache, so that one disk processes read requests, while the other disk is processing a write batch according to the CSCAN policy. We propose an improved scheduling policy as follows: (i) eliminating the forced idleness caused by the batch processing paradigm for write requests, i.e., allowing write requests to be processed individually; (ii) using SATF or even an exhaustive search, to reduce destaging time compared to CSCAN; (iii) introducing a threshold for the number of read requests, which when exceeded defers the destaging of dirty blocks. We compare these two scheduling policies with each other and also against prioritizing the processing of reads versus writes: (i) the head-of-the-line (HOL) priority queueing discipline, (ii) SATF with conditional priorities. It follows from simulation results that the new method outperforms Polyzois' method, which is even outperformed by the HOL priority policy. SATF with conditional priorities slightly outperforms the proposed method from the viewpoint of its throughput and response time, but is susceptible to more variability in response time.

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“…Disk scheduling algorithms also play an important role in reducing the performance gap between processors and disk I/O [Coffman and Hofri 1990;Jacobson and Wilkes 1991;Seltzer et al 1990;Yu et al 1993]. The shortestseek-time-first (SSTF) algorithm is efficient in minimizing seek times, but starvation-bound and unfair in nature [Denning 1967].…”

Section: Related Workmentioning

confidence: 98%

Modeling and improving security of a local disk system for write-intensive workloads

2006

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Since security is of critical importance for modern storage systems, it is imperative to protect stored data from being tampered with or disclosed. Although an increasing number of secure storage systems have been developed, there is no way to dynamically choose security services to meet disk requests' flexible security requirements. Furthermore, existing security techniques for disk systems are not suitable to guarantee desired response times of disk requests. We remedy this situation by proposing an adaptive strategy (referred to as AWARDS) that can judiciously select the most appropriate security service for each write request, while endeavoring to guarantee the desired response times of all disk requests. To prove the efficiency of the proposed approach, we build an analytical model to measure the probability that a disk request is completed before its desired response time. The model also can be used to derive the expected value of disk requests' security levels. Empirical results based on synthetic workloads as well as real I/O-intensive applications show that AWARDS significantly improves overall performance over an existing scheme by up to 358.9% (with an average of 213.4%).

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Queueing models of secondary storage devices

Cited by 20 publications

References 37 publications

Mirrored disk rouing and scheduling

Mirrored disk rouing and scheduling

Performance Comparison of Mirrored Disk Scheduling Methods with a Shared Non-Volatile Cache

Modeling and improving security of a local disk system for write-intensive workloads

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