Independent Disks Research Articles

Design and Implementation of SSD-Assisted Backup and Recovery for Database Systems

As flash-based solid-state drive (SSD) becomes more prevalent because of the rapid fall in price and the significant increase in capacity, customers expect better data services than traditional disk-based systems. However, the order of magnitude performance provided and new characteristics of flash require a rethinking of data services. For example, backup and recovery is an important service in a database system since it protects data against unexpected hardware and software failures. To provide backup and recovery, backup/recovery tools or backup/recovery methods by operating systems can be used. However, the tools perform time-consuming jobs, and the methods may negatively affect run-time performance during normal operation even though high-performance SSDs are used. To handle these issues, we propose an SSD-assisted backup/recovery scheme for database systems. Our scheme is to utilize the characteristics (e.g., out-of-place update) of flash-based SSD for backup/recovery operations. To this end, we exploit the resources (e.g., flash translation layer and DRAM cache with supercapacitors) inside SSD, and we call our SSD with new backup/recovery functionality BR-SSD. We design and implement the functionality in the Samsung enterprise-class SSD (i.e., SM843Tn) for more realistic systems. Furthermore, we exploit and integrate BR-SSDs into database systems (i.e., MySQL) in replication and redundant array of independent disks (RAID) environments, as well as a database system in a single BR-SSD. The experimental result demonstrates that our scheme provides fast backup and recovery but does not negatively affect the run-time performance during normal operation.

The Design of Power Security Defense System Based on Resource Pool Cloud Computing Technology

In order to realize the power system defense security, this article puts forward the idea and method of constructing power dispatching automation systems with a cloud computing architecture and realizes the unified management of distributed resources with server virtualization technology. Real-time online migration of each module of the scheduling system is realized by using the in-memory data transfer technology. The multi-node network heartbeat detection technology is used to realize the complete monitoring of the server cluster. In the form of an independent disk array, the fault node is removed, and the service is restored automatically. The whole disaster reserve of the system is realized by means of remote resource mapping. System analysis results show that compared with traditional architecture, the service interruption probability of the new scheduling automation system is effectively reduced. Fault redundancy capacity in the station is increased from a key module 2 node to multi-node protection of all modules.

Balancing Reliability and Cost in Cloud-RAID Systems with Fault-Level Coverage

Based on redundancy techniques, cloud-RAIDs (Redundant Array of Independent Disks) offer an effective storage solution to achieve high data reliability. Their performance however can be greatly hindered by the fault-level coverage (FLC) behavior, where an uncovered disk fault may crash the entire system in spite of adequate redundancy remaining. Moreover, different choices of cloud disk providers lead to designs with different overall reliability and cost. Thus, in this paper we formulate and solve optimization problems, which determine the combination of cloud disks (from different providers) maximizing the cloud-RAID system reliability or minimizing the total cost. The cloud-RAID reliability is analyzed using a combinatorial and analytical modeling method while considering effects of the FLC behavior. Multiple case studies are performed to demonstrate the considered optimization problems and proposed solution methodology.

Fault‐level coverage analysis of multistate cloud‐RAID storage systems

In this paper, a multistate cloud‐RAID (redundant array of independent disks) storage system subject to fault‐level coverage (FLC) is modeled and analyzed. Most of the existing works on reliability analysis of cloud‐RAID systems have either assumed binary‐state for storage disks or failed to consider imperfect fault coverage, an inherent behavior of fault‐tolerant systems. This work advances the state of the art by proposing a combinatorial method based on multivalued decision diagrams for analyzing reliability of a multistate cloud‐RAID system with FLC. The FLC is one common type of imperfect fault coverage behaviors, where the system fault recovery capability is dependent on the number of disk faults happening within a certain recovery window. Effects of the functional dependence behavior between the RAID controller and disks are addressed. The method is illustrated through a detailed analysis of an example cloud‐RAID 5 storage system. Numerical results are provided to show the impact of different design parameters on system performance. These results also demonstrate that failure to consider FLC leads to inaccurate system state probabilities, further misleading system design activities based on these probabilities such as maintenance and optimization.

Optimizing Imperfect Coverage Cloud-RAID Systems Considering Reliability and Cost

This paper considers a cloud provider selection problem to optimize the cloud-redundant array of independent disks (RAID) storage system subject to imperfect coverage (IPC), where an uncovered disk fault causes extensive damages to the entire system despite the presence of adequate redundancy. Given available cloud storage disk providers with disks having different costs, failure parameters and coverage factors, the objective of the optimal design is to select the combination of cloud providers minimizing system unreliability or cost. Both unconstrained and constrained optimization problems are considered. The solution methodology encompasses an analytical, combinatorial method for reliability analysis of the considered cloud-RAID storage system with the IPC behavior. Based on practical design parameters, the brute force approach is utilized to obtain the optimal design configuration. Several case studies are provided to illustrate the proposed optimization problems and solution method.

The Clinical Predictive Value of the Neutrophil to Lymphocyte Ratio as a Biomarker in Lumbar Disc Herniation

Objective: Low back pain is a frequently seen problem in the society and causes loss of labor. Although etiology of lumbar disc herniation is multi-factorial it is known that it is determinant for the etiology of intervertebral disc degeneration herniation. In recent studies, it has been shown that it has an efficient role in the process of inflamation and inflamatory cytokine disc. We aimed to investigate the association between the neutrophil to Lymphocyte Ratio level as an inflammatory biomarker in patients with lumbar disc herniation. Methods: 394 patients between the age of 18-80 applying to our center because of low back pain complaint and having lumbar MR were included in the study. The patients were divided into two groups as having lumbar disc hernia and not having based on the lumbar MR result. Blood samples were taken from all patients during application and neutrophil lymphocyte rates were calculated. Results. Average age of group with lumbar disc hernia was 46 and 55 of these cases were female and 45 of them were male. N/L rate was measured as 3.81+/-1.85 (p=0.001) in the group having lumbar disc hernia and significant difference compared to the control group was noted. It was found out that lifting weight (β=0.121 95% Cl (0.052-0.281), P<0.001),BMI (β=0.226, 95% Cl (0.080-0.640) P=0.005), DM (β=0.268 95% Cl (0.074-0.969), P=0.045), smoking (β=3.226 95% Cl (1,343-7.749), P<0.009), educational background (β=5.268 95% Cl (1.941-9.796), P=0.001) and NLR (β=1.302 95% Cl (1.013-1.673), P=0.039) were the independent predictors in the presence of lumbar disc herniation. Conclusion: NLR may be used as a simple and reliable premise independent predictor of lumbar disc herniation in patients with low back pain.

Popularity-Based Online Scaling for RAID Systems Under General Settings

The ever-increasing demand of storage capacity and system performance leads to the scaling requirement in redundant arrays of independent disks (RAID)-structured storage systems. Existing approaches mainly focus on minimizing data migration in offline scenario, but not consider the user accesses issued by applications. However, in online scenario, the scaling I/Os and user I/Os usually interfere with each other, and result in significant performance degradation. Thus, it is of big significance to develop an efficient online scaling scheme to mitigate the impact of I/O interference. In this paper, we propose popularity-based online scaling (POS), which exploits workload locality by scaling storage zones with high popularity in a higher priority. POS can efficiently alleviate the interference between scaling I/Os and user I/Os, and it is also general enough to scale various RAID systems like RAID-0, RAID-5, and RAID-6. It can also be readily deployed atop various conventional RAID scaling approaches to improve their performance. To demonstrate the effectiveness of POS, we implement various conventional RAID scaling approaches, and also implement POS on top of these approaches for comparison. Extensive simulations with real-world workloads show that POS can efficiently reduce the response time of user requests and scaling I/Os, and also improves the sequentiality of data accesses.

RAID 4SMR: RAID Array with Shingled Magnetic Recording Disk for Mass Storage Systems

One way to increase storage density is using a shingled magnetic recording (SMR) disk. We propose a novel use of SMR disks with RAID (redundant array of independent disks) arrays, specifically building upon and compared with a basic RAID 4 arrangement. The proposed scheme (called RAID 4SMR) has the potential to improve the performance of a traditional RAID 4 array with SMR disks. Our evaluation shows that compared with the standard RAID 4, when using update in-place in RAID arrays, RAID 4SMR with garbage collection not just can allow the adoption of SMR disks with a reduced performance penalty, but offers a performance improvement of up to 56%.

Classified enhancement model for big data storage reliability based on Boolean satisfiability problem

Disk reliability is a serious problem in the big data foundation environment. Although the reliability of disk drives has greatly improved over the past few years, they are still the most vulnerable core components in the server. If they fail, the result can be catastrophic: it can take some days to recover data, sometimes data lost forever. These are unacceptable for some important data. XOR parity is a typical method to generate reliability syndrome, thus improving the reliability of the data. In practice, we find that the data is still likely to be lost. In most storage systems reliability improvements are achieved through the allocation of additional disks in Redundant Arrays of Independent Disks (RAID), which will increase the hardware costs, thus it will be very difficult for cost-constrained environments. Therefore, how to improve the data integrity without raising the hardware cost has aroused much interest of big data researchers. This challenge is when creating non-traditional RAID geometries, care must be taken to respect data dependence relationships to ensure that the new RAID strategy improves reliability, which is a NP-hard problem. In this paper, we present an approach for characterizing these challenges using high-dimension variants of the n-queens problem that enables performable solutions via the SAT solver MiniSAT, and use the greedy algorithm to analyze the queen’s attack domain, as a basis for reliability syndrome generation. A large number of experiments show that the approach proposed in this paper is feasible in software-defined data centers and the performance of the algorithm can meet the current requirements of the big data environment.

Joint Decoder Design for SSDs

Error-correction codes (ECC) and redundant array of independent disks (RAID) are commonly used to protect NAND-based solid state drives (SSD) from serious noise/disturb. In order to tolerate more errors, common solutions are more complex ECCs and RAIDs. Meanwhile, due to the error-correction mechanisms and flash translation layer, NAND-based SSDs inevitably generate abundant redundant information. The theme of this paper is to show that instead of designing new error correction mechanisms from scratch, the NAND-based SSD reliability can be greatly improved by utilizing current decoders to explore the inherent information between redundant pages. We first propose a joint decoder to recover multiple pages by utilizing redundant pages within a stripe of ECC/RAID, and then we consider a joint decoder to recover multiple pages by utilizing write-amplified (WA) pages. The simulation results show that with the proposed algorithm, a performance gain of as much as 1.8 dB can be obtained. The theoretical study reveals that the joint decoding model can be studied from the perspective of relay channel model, and this helps to explore how much information can be reliably stored with the RAID/WA system in SSD.

The Mass Evolution of Protostellar Disks and Envelopes in the Perseus Molecular Cloud

Abstract In the standard picture for low-mass star formation, a dense molecular cloud undergoes gravitational collapse to form a protostellar system consisting of a new central star, a circumstellar disk, and a surrounding envelope of remaining material. The mass distribution of the system evolves as matter accretes from the large-scale envelope through the disk and onto the protostar. While this general picture is supported by simulations and indirect observational measurements, the specific timescales related to disk growth and envelope dissipation remain poorly constrained. In this paper we conduct a rigorous test of a method introduced by Jørgensen et al. to obtain mass measurements of disks and envelopes around embedded protostars with observations that do not resolve the disk (resolution of ∼1000 au). Using unresolved data from the recent Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, we derive disk and envelope mass estimates for 59 protostellar systems in the Perseus molecular cloud. We compare our results to independent disk mass measurements from the VLA Nascent Disk and Multiplicity survey and find a strong linear correlation, suggesting that accurate disk masses can be measured from unresolved observations. Then, leveraging the size of the MASSES sample, we find no significant trend in protostellar mass distribution as a function of age, as approximated from bolometric temperatures. These results may indicate that the disk mass of a protostar is set near the onset of the Class 0 protostellar stage and remains roughly constant throughout the Class I protostellar stage.

Convergence of the free Boltzmann quadrangulation with simple boundary to the Brownian disk

Nous démontrons que la quadrangulation de Boltzmann libre avec un bord simple de périmètre fixé, munie de sa métrique de graphe, de sa mesure d’aire naturelle, et du chemin qui décrit sa frontière, converge dans la limite d’échelle vers le disque brownien libre de Boltzmann. La topologie de cette convergence est celle de Gromov–Hausdorff–Prokhorov-uniforme (GHPU), qui est l’analogue naturel de la topologie de Gromov-Hausdroff pour des espaces métriques mesurés décorés par une courbe. Nous déduisons de cela qu’une quadrangulation aléatoire de la sphère, décorée par une marche aléatoire auto-évitante de longueur $2l$, converge en loi pour la topologie GHPU vers l’espace métrique mesuré et décoré par une courbe que l’on obtient en recollant ensemble deux disques browniens indépendants le long de leurs bords.

Brownian disks and the Brownian snake

Nous donnons une nouvelle construction des disques browniens, qui ont ete definis par Bettinelli et Miermont comme limites d’echelle de quadrangulations avec frontiere quand la taille de la frontiere tend vers l’infini. Notre methode est semblable a la construction de la carte brownienne, mais elle utilise la mesure d’excursion positive du serpent brownien introduite recemment. Cette mesure d’excursion implique un arbre aleatoire continu dont les sommets recoivent des labels positifs, qui correspondent aux distances depuis la frontiere dans notre approche du disque brownien. Nous donnons plusisurs applications de cette construction. En particulier, nous montrons que la mesure uniforme sur la frontiere peut etre obtenue comme limite de la mesure de volume (convenablement normalisee) sur un petit voisinage tubulaire de la frontiere. Nous montrons aussi que les composantes connexes du complementaire du filet brownien sont des disques browniens, comme cela est suggere dans le travail recent de Miller et Sheffield. Finalement, nous montrons que les composantes connexes du complementaire d’une boule centree au point distingue de la carte brownienne sont, conditionnellement a leurs volumes et leurs perimetres, des disques browniens independants.

Improving 3D NAND Flash Memory Lifetime by Tolerating Early Retention Loss and Process Variation

Compared to planar (i.e., two-dimensional) NAND flash memory, 3D NAND flash memory uses a new flash cell design, and vertically stacks dozens of silicon layers in a single chip. This allows 3D NAND flash memory to increase storage density using a much less aggressive manufacturing process technology than planar NAND flash memory. The circuit-level and structural changes in 3D NAND flash memory significantly alter how different error sources affect the reliability of the memory. In this paper, through experimental characterization of real, state-of-the-art 3D NAND flash memory chips, we find that 3D NAND flash memory exhibits three new error sources that were not previously observed in planar NAND flash memory: (1) layer-to-layer process variation, a new phenomenon specific to the 3D nature of the device, where the average error rate of each 3D-stacked layer in a chip is significantly different; (2) early retention loss, a new phenomenon where the number of errors due to charge leakage increases quickly within several hours after programming; and (3) retention interference, a new phenomenon where the rate at which charge leaks from a flash cell is dependent on the data value stored in the neighboring cell. Based on our experimental results, we develop new analytical models of layer-to-layer process variation and retention loss in 3D NAND flash memory. Motivated by our new findings and models, we develop four new techniques to mitigate process variation and early retention loss in 3D NAND flash memory. Our first technique, Layer Variation Aware Reading (LaVAR), reduces the effect of layer-to-layer process variation by fine-tuning the read reference voltage separately for each layer. Our second technique, Layer-Interleaved Redundant Array of Independent Disks (LI-RAID), uses information about layer-to-layer process variation to intelligently group pages under the RAID error recovery technique in a manner that reduces the likelihood that the recovery of a group fails significantly earlier than the recovery of other groups. Our third technique, Retention Model Aware Reading (ReMAR), reduces retention errors in 3D NAND flash memory by tracking the retention time of the data using our new retention model and adapting the read reference voltage to data age. Our fourth technique, Retention Interference Aware Neighbor-Cell Assisted Correction (ReNAC), adapts the read reference voltage to the amount of retention interference a page has experienced, in order to re-read the data after a read operation fails. These four techniques are complementary, and can be combined together to significantly improve flash memory reliability. Compared to a state-of-the-art baseline, our techniques, when combined, improve flash memory lifetime by 1.85×. Alternatively, if a NAND flash vendor wants to keep the lifetime of the 3D NAND flash memory device constant, our techniques reduce the storage overhead required to hold error correction information by 78.9%.

Angular Momentum and Galaxy Formation Revisited: Scaling Relations for Disks and Bulges

Abstract We show that the stellar specific angular momentum j ⋆, mass M ⋆, and bulge fraction of normal galaxies of all morphological types are consistent with a simple model based on a linear superposition of independent disks and bulges. In this model, disks and bulges follow scaling relations of the form and with but offset from each other by a factor of 8 ± 2 over the mass range . Separate fits for disks and bulges alone give and , respectively. This model correctly predicts that galaxies follow a curved 2D surface in the 3D space of , , and . We find no statistically significant indication that galaxies with classical and pseudo bulges follow different relations in this space, although some differences are permitted within the observed scatter and the inherent uncertainties in decomposing galaxies into disks and bulges. As a byproduct of this analysis, we show that the j ⋆–M ⋆ scaling relations for disk-dominated galaxies from several previous studies are in excellent agreement with each other. In addition, we resolve some conflicting claims about the dependence of the j ⋆–M ⋆ scaling relations. The results presented here reinforce and extend our earlier suggestion that the distribution of galaxies with different in the j ⋆–M ⋆ diagram constitutes an objective, physically motivated alternative to subjective classification schemes such as the Hubble sequence.

A Unified Form of EVENODD and RDP Codes and Their Efficient Decoding

Array codes are used widely in data storage systems such as redundant array of independent disks. The row-diagonal parity (RDP) codes and EVENODD codes are two popular double-parity array codes. The increasing capacity of hard disks demands better fault tolerance by using array codes with three or more parity disks. Although many extensions of RDP and EVENODD codes have been proposed, their main drawback is high decoding complexity. In this paper, we propose a unified form of RDP and EVENODD codes under which RDP codes can be treated as shortened EVENODD codes. Moreover, an efficient decoding algorithm based on an LU factorization of a Vandermonde matrix is proposed. The LU decoding method is applicable to all the erasure patterns of RDP and EVENODD codes with three parity columns. It is also applicable to the erasure decoding of RDP and EVENODD codes with more than three parity columns when the number of continuous surviving parity columns is no less than the number of erased information columns and the first parity column has not failed. The proposed efficient decoding algorithm is also applicable to other Vandermonde array codes, with less decoding complexity than that of the existing method.

WARD: Wear Aware RAID Design Within SSDs

Redundant arrays of independent disk (RAID) is an efficient approach to relieve reliability sacrifice caused by aggressive scale-out of solid state drives (SSDs). Unfortunately, RAID is unfriendly to SSDs due to redundant parity write and data rebuilding. This paper proposes a wear aware RAID design for SSDs, called WARD , which: 1) adaptively organizes RAID stripes according to real-time interblock unbalanced wear for relieving high performance and storage overhead caused by parity data and 2) migrates blocks about to break in advance and leaves these blocks unused to reduce data rebuilding overhead. An efficient block wear detection scheme is employed to detect block wear during the whole lifetime of SSDs. Beginning with a large stripe width RAID instead of the redundant worst-case RAID, WARD reorganizes RAID stripes once wear blocks with high bit error rates come out. WARD divides the original stripe into several short width RAID stripes according to the number of wear blocks and separates all wear blocks into different stripes. This not only reduces parity redundancy but also provides high reliability to avoid more than RAID recoverable error-prone chunks remaining in one stripe. For high wear blocks tending to wear-out, data in them are migrated in advance and then the blocks are left unused, which efficiently avoids performance shock caused by data rebuilding. A reliability model considering interblock unbalanced wear is proposed and reveals that WARD provides a high and stable reliability and greatly prolongs the lifetime of SSDs. Comprehensive experiments based on an SSDsim derivative simulator are carried out and experiment results show that WARD considerably improves system performance compared to the worst-case RAID.

Improving the Update Complexity of Locally Repairable Codes

Locally repairable codes (LRCs) have been recently proposed and used in real-world distributed storage systems (DSSs) such as Microsoft Azure Storage and Facebook HDFS-RAID (Hadoop Distributed File System-Redundant Array of Independent Disks). Since information in DSSs is changed frequently, reducing update complexity (UC) of LRCs is of great interest. In this paper, we propose code design algorithms that can reduce UC of existing LRCs without sacrificing their important code parameters such as minimum distance, code rate, or locality. We establish bounds on UC, and use them to show that our algorithms can achieve optimal or near optimal UC for a large class of LRCs.

Modeling Impact of Human Errors on the Data Unavailability and Data Loss of Storage Systems

Data storage systems (DSSs) and their availability play a crucial role in contemporary datacenters. Despite using mechanisms such as automatic failover in datacenters, the role of human agents and consequently their destructive errors is inevitable. Due to very large number of disk drives used in exascale datacenters and their high failure rates, the disk subsystem in storage systems has become a major source of data unavailability (DU) and data loss (DL) initiated by human errors. In this paper, we investigate the effect of incorrect disk replacement service (IDRS) on the availability and reliability of DSSs. To this end, we analyze the consequences of IDRS in a disk array, and conduct Monte Carlo simulations to evaluate DU and DL during mission time. The proposed modeling framework can cope with different storage array configurations and data object survivability , representing the effect of system-level redundancies such as remote backups and mirrors. In the proposed framework, the model parameters are obtained from industrial and scientific reports alongside field data, which have been extracted from a datacenter operating with 70 storage racks. The results show that ignoring the impact of IDRS leads to unavailability underestimation by up to three orders of magnitude. Moreover, our study suggests that by considering the effect of human errors, the conventional beliefs about the dependability of different redundant array of independent disks (RAID) mechanisms should be revised. The results show that $\text{RAID}1$ can result in lower availability compared to $\text{RAID}5$ in the presence of human errors. The results also show that employing automatic fail-over policy (using hot spare disks) can reduce the drastic impacts of human errors by two orders of magnitude.

Lifespan Analysis for Redundant Array of Independent Module Based Solid State Drives

Solid state drives (SSD) are usually built using a NAND flash memory array. An SSD controller manages datastreams stripped to multiple flash memory channels. The device could be regarded as a level-0 structure of redundant array of independent disk (RAID), the technical term for a disk array system. This typical SSD controller architecture is called an intrinsic RAID (iRAID). An iRAID-based SSD controller has to execute sophisticated wear-leveling algorithms and dynamically calculate the lifespan of each flash memory chip as well as run error correction coding. redundant array of independent module (RAIM) was proposed to simplify the SSD controller by applying a group of standardized memory modules instead of raw flash memory chips. One of the widely recognized memory modules is the embedded multi-media card (eMMC) module, which is a small component, typically with a ball grid array package, and is found in consumer applications. In the paper, we have described the methods needed to optimize wear-leveling in an array of eMMC modules and deduced a formula to evaluate and optimize the lifespan of an RAIM-based SSD. A silicon SSD controller was implemented to verify the analysis. The positive result revealed that the lifespan of the RAIM-based SSD could be improved in consumer-grade eMMC modules.