Evaluating the Impact of Irrecoverable Read Errors on Disk Array Reliability

Pâris, J.-F.; Amer, Ahmed; Long, Darrell D. E.; Schwarz, Thomas

doi:10.1109/prdc.2009.66

Cited by 8 publications

(5 citation statements)

References 13 publications

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“…They express reliability as the mean-time-to-data loss (MTTDL) for D+1 and D+2 configurations [Dholakia et al 2006;EMC 2007;Gao et al 2010;Oracle 2010;Paris et al 2009; Serve The Home 2011], the number of data loss events over time [Elerath and Pecht 2009;Rao et al 2006], or use a normalized magnitude of data loss as a replacement for MTTDL.…”

Section: Previous Workmentioning

confidence: 99%

Beyond MTTDL

Elerath

Schindler

2014

ACM Trans. Storage

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We introduce a new closed-form equation for estimating the number of data-loss events for a redundant array of inexpensive disks in a RAID-6 configuration. The equation expresses operational failures, their restorations, latent (sector) defects, and disk media scrubbing by time-based distributions that can represent non-homogeneous Poisson processes. It uses two-parameter Weibull distributions that allows the distributions to take on many different shapes, modeling increasing, decreasing, or constant occurrence rates. This article focuses on the statistical basis of the equation. It also presents time-based distributions of the four processes based on an extensive analysis of field data collected over several years from 10,000s of commercially available systems with 100,000s of disk drives. Our results for RAID-6 groups of size 16 indicate that the closed-form expression yields much more accurate results compared to the MTTDL reliability equation and matching computationally-intensive Monte Carlo simulations.

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Section: Previous Workmentioning

confidence: 99%

Beyond MTTDL

Elerath

Schindler

2014

ACM Trans. Storage

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“…In addition, clean drives will develop sector failures at rate λ , and we scrub the drives to remove the sector errors at rate µ . This model was studied in [5], and the approach here is similar but generalized to an arbitrary number of check drives. Figure 7 depicts the Markov chain for the M = 2 cases, and Table 1 gives the transition rates between states in the general case.…”

Section: Model 5: Sector Errorsmentioning

confidence: 99%

“…However this graph shows that the consideration of sector errors yields an estimate of PDL 5 that is several orders of magnitude higher than the model proposed in Section 4. [5] discusses extensively the benefits of shorter scrubbing intervals (increased µ ), finding that more frequent scrubbing can substantially increase the MTTDL of the system and thus make it more reliable. We find that scrubbing more frequently can indeed increase the reliability of the system, but the effect is much less dramatic than adding another check drive.…”

Section: Transitionmentioning

confidence: 99%

On the Reliability of RAID Systems: An Argument for More Check Drives

Mann,

Anderson,

Rychlik

2012

Preprint

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In this paper we address issues of reliability of RAID systems. We focus on "big data" systems with a large number of drives and advanced error correction schemes beyond RAID 6. Our RAID paradigm is based on Reed-Solomon codes, and thus we assume that the RAID consists of N data drives and M check drives. The RAID fails only if the combined number of failed drives and sector errors exceeds M, a property of Reed-Solomon codes.We review a number of models considered in the literature and build upon them to construct models usable for a large number of data and check drives. We attempt to account for a significant number of factors that affect RAID reliability, such as drive replacement or lack thereof, mistakes during service such as replacing the wrong drive, delayed repair, and the finite duration of RAID reconstruction. We evaluate the impact of sector failures that do not result in drive replacement.The reader who needs to consider large M and N will find applicable mathematical techniques concisely summarized here, and should be able to apply them to similar problems. Most methods are based on the theory of continuous time Markov chains, but we move beyond this framework when we consider the fixed time to rebuild broken hard drives, which we model using systems of delay and partial differential equations.One universal statement is applicable across various models: increasing the number of check drives in all cases increases the reliability of the system, and is vastly superior to other approaches of ensuring reliability such as mirroring.

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“…investigated a RAID level 6 array with six disks and concluded that scheduling scrubbing scans once a month instead of once a year can increase the MTTDL of the array from 600 to almost 1,000 percent depending on the disk repair time [15].…”

Section: Data Lossmentioning

confidence: 99%

Improving Disk Array Reliability Through Expedited Scrubbing

Pâris

Schwarz

Amer

et al. 2010

2010 IEEE Fifth International Conference on Networking, Architecture, and Storage

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Abstract-Disk scrubbing periodically scans the contents of a disk array to detect the presence of irrecoverable read errors and reconstitute the contents of the lost blocks using the builtin redundancy of the disk array. We address the issue of scheduling scrubbing runs in disk arrays that can tolerate two disk failures without incurring a data loss, and propose to start an urgent scrubbing run of the whole array whenever a disk failure is detected. Used alone or in combination with periodic scrubbing runs, these expedited runs can improve the mean time to data loss of disk arrays over a wide range of disk repair times. As a result, our technique eliminates the need for frequent scrubbing runs and the need to maintain spare disks and personnel on site to replace failed disks within a twentyfour hour interval.

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Evaluating the Impact of Irrecoverable Read Errors on Disk Array Reliability

Cited by 8 publications

References 13 publications

Beyond MTTDL

Beyond MTTDL

On the Reliability of RAID Systems: An Argument for More Check Drives

Improving Disk Array Reliability Through Expedited Scrubbing

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