Redundant Array Of Independent Disks System Research Articles

Survivability and Vulnerability Analysis of Cloud RAID Systems under Disk Faults and Attacks

In this paper we model and analyze survivability and vulnerability of a cloud RAID (Redundant Array of Independent Disks) storage system subject to disk faults and cyber-attacks. The cloud RAID survivability is concerned with the system’s ability to function correctly even under the circumstance of hazardous behaviors including disk failures and malicious attacks. The cloud RAID invulnerability is concerned with the system’s ability to function correctly while occupying some state immune to malicious attacks. A continuous-time Markov chains-based method is suggested to perform the disk level survivability and invulnerability analysis. Combinatorial methods are then presented for the cloud RAID system level analysis, which can accommodate both homogeneous (based on binomial coefficients) and heterogeneous (based on multi-valued decision diagrams) disks. A detailed case study on a cloud RAID 5 system is conducted to illustrate the application of the proposed methods. Impacts of different parameters on the disk and system survivability and invulnerability are also investigated through numerical analysis.

Generic RAID reassembly using block-level entropy

RAIDs (Redundant Array of Independent Disks) are widely used in storage systems to prevent data loss in case of hardware defects on a hard disk and to improve I/O performance. In case the RAID controller fails or in the context of a forensic investigation, the content of the RAID has to be reconstructed from the single disks or rather from disk images. Due to the variety of RAID controllers and various implementation and configuration possibilities, different parameters that are necessary for reconstruction are often unknown. This might be the case because the original configuration just has not been documented or in the forensic case, the administrator might not be cooperating and not willing to reveal the configuration. Using the original RAID system in such cases is not an option, too, because the original evidence should not be altered. We present a novel approach to automatically detect all parameters to reassemble the logical RAID volume based on block level entropy measurement and generic heuristics. We also provide a performance-optimized open source implementation of our approach that is also able to afterwards reassemble the entire logical RAID volume and to further recover single missing disks using the redundancy information as present in RAID-5.

CSWL: Cross-SSD Wear-Leveling Method in SSD-Based RAID Systems for System Endurance and Performance

Flash memory has limited erasure/program cycles. Hence, to meet their advertised capacity all the time, flash-based solid state drives (SSDs) must prolong their life span through a wear-leveling mechanism. As a very important part of flash translation layer (FTL), wear leveling is usually implemented in SSD controllers, which is called internal wear leveling. However, there is no wear leveling among SSDs in SSD-based redundant array of independent disks (RAIDs) systems, making some SSDs wear out faster than others. Once an SSD fails, reconstruction must be triggered immediately, but the cost of this process is so high that both system reliability and availability are affected seriously. We therefore propose cross-SSD wear leveling (CSWL) to enhance the endurance of entire SSD-based RAID systems. Under the workload of random access pattern, parity stripes suffer from much more updates because updating to a data stripe will cause the modification of other all related parity stripes. Based on this principle, we introduce an age-driven parity distribution scheme to guarantee wear leveling among flash SSDs and thereby prolong the endurance of RAID systems. Furthermore, age-driven parity distribution benefits performance by maintaining better load balance. With insignificant overhead, CSWL can significantly improve both the life span and performance of SSD-based RAID.

A HIERARCHICAL MARKOV RELIABILITY MODEL FOR DATA STORAGE SYSTEMS WITH MEDIA SELF-RECOVERY

A Redundant Array of Independent Disks (RAID) system with n disks or hard drives can be modeled as a k-out-of-n repairable system for which at least k operational disks are required. This paper proposes a hierarchical Markov model to estimate the reliability of RAID systems. The method encompasses Markov models for evaluating the reliability of individual disks at the lower level and the redundant model for evaluating the reliability of entire RAID at the system level. Both hardware and media failures are considered, and the media failures can be potentially recovered via the disk self-restoration mechanism. The system mean-time-to-data-loss is also derived and results are compared to those estimated from system-based Markov models. The major contribution of this work is that the reliability for RAID systems is approached by combining the redundant modeling technique with the single disk-based Markov model, thus simplifying the computational efforts. The proposed method is applied on RAID-5 and RAID-6 systems to demonstrate the applicability and performance of the new model.

動的Ｗｅｂアプリケーションとクラスタリング技術を実装した医用画像配信システムの開発と評価

It has been noted that the downtime of medical informatics systems is often long. Many systems encounter downtimes of hours or even days, which can have a critical effect on daily operations. Such systems remain especially weak in the areas of database and medical imaging data. The scheme design shows the three-layer architecture of the system: application, database, and storage layers. The application layer uses the DICOM protocol (Digital Imaging and Communication in Medicine) and HTTP (Hyper Text Transport Protocol) with AJAX (Asynchronous JavaScript+XML). The database is designed to decentralize in parallel using cluster technology. Consequently, restoration of the database can be done not only with ease but also with improved retrieval speed. In the storage layer, a network RAID (Redundant Array of Independent Disks) system, it is possible to construct exabyte-scale parallel file systems that exploit storage spread. Development and evaluation of the test-bed has been successful in medical information data backup and recovery in a network environment. This paper presents a schematic design of the new medical informatics system that can be accommodated from a recovery and the dynamic Web application for medical imaging distribution using AJAX.

Queueing models of RAID systems with maxima of waiting times

A queueing model is developed that approximates the effect of synchronizations at parallel service completion instants. Exact results are first obtained for the maxima of independent exponential random variables with arbitrary parameters, and this is followed by a corresponding approximation for general random variables, which reduces to the exact result in the exponential case. This approximation is then used in a queueing model of RAID (Redundant Array of Independent Disks) systems, in which accesses to multiple disks occur concurrently and complete only when every disk involved has completed. We consider the two most common RAID variants, RAID0-1 and RAID5, as well as a multi-RAID system in which they coexist. This can be used to model adaptive multi-level RAID systems in which the RAID level appropriate to an application is selected dynamically. The random variables whose maximum has to be computed in these applications are disk response times, which are modelled by the waiting times in M / G / 1 queues. To compute the mean value of their maximum requires the second moment of queueing time and we obtain this in terms of the third moment of disk service time, itself a function of seek time, rotational latency and block transfer time. Sub-models for these quantities are investigated and calibrated individually in detail. Validation against a hardware simulator shows good agreement at all traffic intensity levels, including the threshold for practical operation above which performance deteriorates sharply.