Distorted mirrors

Solworth, Jon A.; Orji, Cyril U.

doi:10.1109/pdis.1991.183061

Cited by 16 publications

(6 citation statements)

References 6 publications

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“…These include the large body of work on mirroring systems [Bitton and Gray 1988]. The work on doubly distorted mirrors [Solworth and Orji 1991] creates multiple replicas on master and slave disks to increase both write performance (using initial write-anywhere and background updating of original locations) and read performance by dispatching read requests to the nearest free arm. Zhang et al's work on eager writing [Zhang et al 2002] extended this approach to mirrored/striped RAID configurations primarily for database OLTP workload (which are characterized by little locality or sequentiality).…”

Section: I/o Performance Optimizationmentioning

confidence: 99%

I/O Deduplication

2010

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Duplication of data in storage systems is becoming increasingly common. We introduce I/O Deduplication, a storage optimization that utilizes content similarity for improving I/O performance by eliminating I/O operations and reducing the mechanical delays during I/O operations. I/O Deduplication consists of three main techniques: content-based caching, dynamic replica retrieval, and selective duplication. Each of these techniques is motivated by our observations with I/O workload traces obtained from actively-used production storage systems, all of which revealed surprisingly high levels of content similarity for both stored and accessed data. Evaluation of a prototype implementation using these workloads showed an overall improvement in disk I/O performance of 28 to 47% across these workloads. Further breakdown also showed that each of the three techniques contributed significantly to the overall performance improvement.

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Section: I/o Performance Optimizationmentioning

confidence: 99%

I/O Deduplication

2010

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“…For example, writes in one disk are done in-place, while a write anywhere policy is followed at the other disk [21]. With distorted mirrors a write anywhere policy is used on the secondary disk to minimize positioning time, while the data on the primary disk is written in place, so that efficient sequential accesses are possible [21].…”

Section: Performance Studies Of Mirrored Disksmentioning

confidence: 99%

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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“…However, there have been numerous proposals to improve the performance of write requests. The distorted mirrors method postulates a write anywhere policy on the secondary disk, so as to save a data block as quickly as possible, while minimizing its positioning time, but writes on the primary disk are written in place, in batches to ensure efficient processing [15]. Other variations to improve RAID1 performance have been proposed by the same authors.…”

Section: Introductionmentioning

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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Distorted mirrors

Cited by 16 publications

References 6 publications

I/O Deduplication

I/O Deduplication

Mirrored disk rouing and scheduling

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

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