Doubly distorted mirrors

Orji, Cyril U.; Solworth, Jon A.

doi:10.1145/170036.170082

Cited by 8 publications

(5 citation statements)

References 11 publications

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“…Persistence is important for retaining the locations of on-disk intrinsic and artificially created duplicate content so that this information can be restored and used immediately upon a system restart event. We note that while persistence is useful to retain intelligence that is acquired over a period of time, "continuous persistence" of metadata in I/O Deduplication is not necessary to guarantee the reliability of the system, unlike other systems such as the eager writing disk array [Zhang et al 2002] or doubly distorted mirroring [Orji and Solworth 1993]. In this sense, selective duplication is similar to the opportunistic replication as performed by FS2 [Huang et al 2005] because it tracks updates to replicated data in memory and only guarantees that the primary copy of data blocks are up-to-date at any time.…”

Section: Persistence Of Metadatamentioning

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: Persistence Of Metadatamentioning

confidence: 99%

I/O Deduplication

2010

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“…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]. With doubly distorted mirrors each disk has master and slave partitions [16], so that both disks are symmetric. With improved traditional mirrors the location of backup data blocks is determined via a mathematical formula [17].…”

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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“…To increase the time between failures of a large storage array, data redundancy techniques can be applied [Bitton and Gray 1988;Burkhard and Menon 1993;Chen et al 1994;Gray et al 1990;Hsiao and DeWitt 1990;Orji and Solworth 1993;Park and Balasubramanian 1986;Patterson et al 1988;Savage and Wilkes 1996;Wilkes et al 1996]. By keeping multiple copies of blocks, or through more sophisticated redundancy schemes such as parity-encoding, storage systems can tolerate a (small) fixed number of faults.…”

Section: Introductionmentioning

confidence: 99%

Improving storage system availability with D-GRAID

et al. 2005

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We present the design, implementation, and evaluation of D-GRAID, a gracefully degrading and quickly recovering RAID storage array. D-GRAID ensures that most files within the file system remain available even when an unexpectedly high number of faults occur. D-GRAID achieves high availability through aggressive replication of semantically critical data, and fault-isolated placement of logically related data. D-GRAID also recovers from failures quickly, restoring only live file system data to a hot spare. Both graceful degradation and live-block recovery are implemented in a prototype SCSI-based storage system underneath unmodified file systems, demonstrating that powerful "file-system like" functionality can be implemented within a "semantically smart" disk system behind a narrow block-based interface.

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Doubly distorted mirrors

Cited by 8 publications

References 11 publications

I/O Deduplication

I/O Deduplication

Mirrored disk rouing and scheduling

Improving storage system availability with D-GRAID

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