Log Disk Research Articles

Monodromy and log geometry

A now classical construction due to Kato and Nakayama attaches a topological space (the "Betti realization") to a log scheme over $\mathbf{C}$. We show that in the case of a log smooth degeneration over the standard log disc, this construction allows one to recover the topology of the germ of the family from the log special fiber alone. We go on to give combinatorial formulas for the monodromy and the $d^2$ differentials acting on the nearby cycle complex in terms of the log structures. We also provide variants of these results for the Kummer etale topology. In the case of curves, these data are essentially equivalent to those encoded by the dual graph of a semistable degeneration, including the monodromy pairing and the Picard-Lefschetz formula.

Effect of processing parameters on the quality of red oak flakes

ABSTRACTA lot of volume of red oak (Quercus rubra) is available for use in the manufacture of oriented strand board (OSB) in the Appalachian and Northeast regions of the U.S.A. However, the large amount of fines and low quality of red oak ring-cut flakes produced in industry have restricted their use in commercial OSB products. This study evaluated the effects of log pre-treatment temperature and disc flaker’s knife clearance on the quality of red oak flakes. Experimental results showed that heat treatment was the dominant factor than the flaker’s knife clearance during oak disc-cut flaking. A large amount of high quality oak flakes with acceptable geometry and minimal fines suitable for usage as face furnish on the OSB panel can be produced with a proper log heating treatment before flaking.

LDM

With the explosive growth in data volume, the I/O bottleneck has become an increasingly daunting challenge for big data analytics. Economic forces, driven by the desire to introduce flash-based Solid-State Drives (SSDs) into the high-end storage market, have resulted in hybrid storage systems in the cloud. However, a single flash-based SSD cannot satisfy the performance, reliability, and capacity requirements of enterprise or HPC storage systems in the cloud. While an array of SSDs organized in a RAID structure, such as RAID5, provides the potential for high storage capacity and bandwidth, reliability and performance problems will likely result from the parity update operations. In this article, we propose a Log Disk Mirroring scheme (LDM) to improve the performance and reliability of SSD-based disk arrays. LDM is a hybrid disk array architecture that consists of several SSDs and two hard disk drives (HDDs). In an LDM array, the two HDDs are mirrored as a write buffer that temporally absorbs the small write requests. The small and random write data are written on the mirroring buffer by using the logging technique that sequentially appends new data. The small write data are merged and destaged to the SSD-based disk array during the system idle periods. Our prototype implementation of the LDM array and the performance evaluations show that the LDM array significantly outperforms the pure SSD-based disk arrays by a factor of 20.4 on average, and outperforms HPDA by a factor of 5.0 on average. The reliability analysis shows that the MTTDL of the LDM array is 2.7 times and 1.7 times better than that of pure SSD-based disk arrays and HPDA disk arrays.

Rotated Logging Storage Architectures for Data Centers: Models and Optimizations

We propose Ro tated Lo gging (RoLo), a new logging architecture for parallel disk-based mirrored storage systems for enhanced energy efficiency, which is one of the key concerns in modern data centers. By spreading destaging I/O activities among short idle time slots and proactively reclaiming the stale logging space, RoLo rotates loggers among a logical logging space pool formed collectively from the free storage space available among mirrored disks. We develop three flavors of RoLo, that is, RoLo-P/R/E, to emphasize performance, reliability, and energy efficiency respectively. Without the extra dedicated log disks and the corresponding centralized destaging, RoLo eliminates the additional hardware and energy costs, potential single point of failure and performance bottleneck. Furthermore, RoLo-P/R/E, applied to specific scenes correctly, can prolong the lifecycle of the disks and improve the system's energy efficiency by reducing the disk spin up/down frequency. We propose RoLo-S to further alleviate the performance bottleneck and energy consumption caused by frequent disk head seeks in on-duty logger disks. We have implemented RoLo and RoLo-S on real disk systems. Extensive trace-driven evaluations demonstrate the advantages of the three RoLo schemes over both a RAID10 system with centralized logging architecture and a typical RAID10 system, and the advantages of RoLo-S over RoLo.

Prediction of wood properties for thawed and frozen logs of quaking aspen, balsam poplar, and black spruce from near-infrared hyperspectral images

This study tested the use of near-infrared hyperspectral images to estimate moisture content (MC) and basic specific gravity (BSG) of thawed and frozen logs of three species: quaking aspen, balsam poplar, and black spruce. For each species, more than 90 small 4 cm cubic samples were prepared and subjected to drying steps in both frozen and thawed conditions. At each step, hypercube images and sample weights were recorded to determine MC and BSG of each sample. Partial least squares (PLS) models were calibrated by considering two factors: log state (thawed and frozen conditions) and species, and their combination. With respect to the species, the PLS model accuracy depends on the range of variation in the input data. The model accuracy was the best for black spruce samples that have the lowest range of variation for both MC and BSG, whereas the model accuracy was the lowest for balsam poplar samples that have the highest range of variation for both MC and BSG. With all the data, the accuracy of the MC model worsened, but the accuracy of the BSG model reached a maximum (\( R_{\text{Validation}}^{2} \) = 0.88). The best PLS model was then employed to produce 2D MC and BSG images over the whole log disks. PLS discriminant analysis was also applied to sort the samples according to three MC or BSG classes, the species, and the log state (frozen and thawed). The overall accuracy was higher than 72 % for both the MC and BSG sorting, 86 % for the species sorting, and 97 % for the log state sorting.

Application of an ultrasonic wave propagation field in the quantitative identification of cavity defect of log disc

This study introduced the concept of the ultrasonic propagation field in wood and verified its applicability through experiments conducted on a log disc. A green Betula costata log section was used in the ultrasonic propagation measurements. An ultrasonic wave detector (RSM-SY5) was used to measure the ultrasonic propagation time (UPT) on the cross section of the log sample. After the ultrasonication was completed on the non-defective log, five man-made cavities with diameters of 4, 8, 12, 16 and 20cm were made sequentially in the heart of the same log and utilized in the ultrasonic test. The even UPT values were then approximately outlined as isolines. Based on the UPT isolines, the ultrasonic propagation field in the log disc was simulated using MATLAB software, and the cavity was identified by overlapping the ultrasonic wave fields from different directions. The size of the cavity defect was proven to be effectively determined by overlying the maps of the ultrasonic wave propagation field through a cross section of the wood. The results indicated that the accuracy of detection values for cavity sizes with diameters of 4, 8, 12, 16 and 20cm were 83.2%, 84.8%, 94.0%, 95.8% and 96.2%, respectively.

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

Abstract Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) concerning the TSt and fracture behavior of Norway spruce under various climatic conditions. Thin log disc specimens were studied to simplify the description of the moisture flow in the samples. The specimens designed for TS were acclimatized to a moisture content (MC) of 18% before TSt tests at 20°C, 60°C, and 90°C were carried out. The maximum stress results of the disc simulations by FEM were compared with the experimental strength results at the same temperature levels. There is a rather good agreement between the results of modeling and experiments. The results also illustrate the strong decrease of TSt with increasing temperature at a constant MC level.

MP-RAID: Mirroring and parity protected disk array

Redundant array of inexpensive disk (RAID)10 is known as the most reliable disk array architecture to tolerate up to half of total disk failures, but failure of two disks in the same mirror set still results in data loss. In this paper, we propose a new disk array architecture, mirroring and parity protected RAID (MP-RAID), which combines both mirroring and parity techniques to further improve reliability of disk arrays. The main idea behind MP-RAID is to protect the data by both mirroring and parity techniques: keep two copies of data in the same mirror set and update the parity block in the log disk within the same parity groups. Reliability analysis shows that the reliability of MP-RAID, in terms of mean time to data loss (MTTDL), is much better than RAID10 and RAID5.

Dual actuator logging disk architecture and modeling

In this paper, we present a dual actuator logging disk architecture to minimize write access latencies. We reduce small synchronous write latency using the notion of logging writes, i.e. writing to free sectors near the current disk head location. However, we show through analytic models and simulations that logging writes by itself is not sufficient to reduce write access latencies, particularly in environments with writes to new data and intermixed reads and writes. Therefore, we augment the logging write method with the addition of a second disk actuator. Our models and simulations show that the addition of the second actuator offers significant performance benefits over a normal disk over a wide range of disk access patterns, and comparisons to strictly logging disk architectures show advantages over a range of disk access patterns.

RAPID-Cache-A reliable and inexpensive write cache for high performance storage systems

Modern high performance disk systems make extensive use of nonvolatile RAM (NVRAM) write caches. A single-copy NVRAM cache creates a single point of failure while a dual-copy NVRAM cache is very expensive because of the high cost of NVRAM. This paper presents a new cache architecture called RAPID-Cache for Redundant, Asymmetrically Parallel, and Inexpensive Disk Cache. A typical RAPID-Cache consists of two redundant write buffers on top of a disk system. One of the buffers is a primary cache made of RAM or NVRAM and the other is a backup cache containing a two-level hierarchy: a small NVRAM buffer on top of a log disk. The small NVRAM buffer combines small write data and writes them into the log disk in large sizes. By exploiting the locality property of I/O accesses and taking advantage of well-known Log-structured File Systems, the backup cache has nearly equivalent write performance as the primary RAM cache. The read performance of the backup cache is not as critical because normal read operations are performed through the primary RAM cache and reads from the backup cache happen only during error recovery periods. The RAPID-Cache presents an asymmetric architecture with a fast-write-fast-read RAM being a primary cache and a fast-write-slow-read NVRAM-disk hierarchy being a backup cache. The asymmetrically parallel architecture and an algorithm that separates actively accessed data from inactive data in the cache virtually eliminate the garbage collection overhead, which are the major problems associated with previous solutions such as Log-structured File Systems and Disk Caching Disk. The asymmetric cache allows cost-effective designs for very large write caches for high-end parallel disk systems that would otherwise have to use dual-copy, costly NVRAM caches. It also makes it possible to implement reliable write caching for low-end disk I/O systems since the RAPID-Cache makes use of inexpensive disks to perform reliable caching. Our analysis and trace-driven simulation results show that the RAPID-Cache has significant reliability/cost advantages over conventional single NVRAM write caches and has great cost advantages over dual-copy NVRAM caches. The RAPID-Cache architecture opens a new dimension for disk system designers to exercise trade-offs among performance, reliability, and cost.

Dynamic parity logging disk arrays for engineering database systems

RAID (redundant arrays of inexpensive disks) has gained much attention in the recent development of fast I/O systems. Of the five levels, the traditional mirrored disk array still provides the highest I/O rate for small ‘write’ transfers. This is because the mirrored disk array has no small ‘write’ problem which is found in other levels of RAID. The authors propose a novel RAID architecture for fast engineering database systems, called dynamic parity logging (DPL) disk array. DPL disk array has no small ‘write’ problem and can provide much higher ‘write’ throughput than other RAID architectures. DPL disk array also has journalling capability, which means that some older design versions are kept for future references. A queueing model for DPL disk array is built. Analytical results, supported by simulation, show that the DPL disk array can provide the highest ‘write’ throughput when compared to RAID levels 1, 4, and 5.

DCD —disk caching disk

This paper presents a novel disk storage architecture called DCD, Disk Caching Disk, for the purpose of optimizing I/O performance. The main idea of the DCD is to use a small log disk, referred to as cache-disk, as a secondary disk cache to optimize write performance. While the cache-disk and the normal data disk have the same physical properties, the access speed of the former differs dramatically from the latter because of different data units and different ways in which data are accessed. Our objective is to exploit this speed difference by using the log disk as a cache to build a reliable and smooth disk hierarchy. A small RAM buffer is used to collect small write requests to form a log which is transferred onto the cache-disk whenever the cache-disk is idle. Because of the temporal locality that exists in office/engineering work-load environments, the DCD system shows write performance close to the same size RAM (i.e. solid-state disk) for the cost of a disk. Moreover, the cache-disk can also be implemented as a logical disk in which case a small portion of the normal data disk is used as the log disk. Trace-driven simulation experiments are carried out to evaluate the performance of the proposed disk architecture. Under the office/engineering work-load environment, the DCD shows superb disk performance for writes as compared to existing disk systems. Performance improvements of up to two orders of magnitude are observed in terms of average response time for write operations. Furthermore, DCD is very reliable and works at the device or device driver level. As a result, it can be applied directly to current file systems without the need of changing the operating system.

Parity logging disk arrays

Parity-encoded redundant disk arrays provide highly reliable, cost-effective secondary storage with high performance for reads and large writes. Their performance on small writes, however, is much worse than mirrored disks—the traditional, highly reliable, but expensive organization for secondary storage. Unfortunately, small writes are a substantial portion of the I/O workload of many important, demanding applications such as on-line transaction processing. This paper presents parity logging , a novel solution to the small-write problem for redundant disk arrays. Parity logging applies journalling techniques to reduce substantially the cost of small writes. We provide detailed models of parity logging and competing schemes—mirroring, floating storage, and RAID level 5—and verify these models by simulation. Parity logging provides performance competitive with mirroring, but with capacity overhead close to the minimum offered by RAID level 5. Finally, parity logging can exploit data caching more effectively than all three alternative approaches.

Distributed logging for transaction processing

Increased interest in using workstations and small processors for distributed transaction processing raises the question of how to implement the logs needed for transaction recovery. Although logs can be implemented with data written to duplexed disks on each processing node, this paper argues there are advantages if log data is written to multiple log server nodes. A simple analysis of expected logging loads leads to the conclusion that a high performance, microprocessor based processing node can support a log server if it uses efficient communication protocols and low latency, non volatile storage to buffer log data. The buffer is needed to reduce the processing time per log record and to increase throughput to the logging disk. An interface to the log servers using simple, robust, and efficient protocols is presented. Also described are the disk data structures that the log servers use. This paper concludes with a brief discussion of remaining design issues, the status of a prototype implementation, and plans for its completion.

Elm Bark Beetle Mortality on Lab-Sprayed Bark Chips, 1978

Abstract Suspended from the edge of a horizontally rotating 27 inch bicycle wheel, four 35 mm x 35 mm elm bark chips were sprayed with an insecticide during 1 pass before a compressed air paint spray gun beneath the wheel axle. The gun delivered 2.2 ml/sec and the wheel turned 4 rpm. This apparatus was in the opening of a laboratory evacuation hood. Bark chips, including some sapwood, had been cut with a band saw from 100 mm dia log disks from a recently felled tree. When each sprayed chip was nearly dry it was dropped into a 0.5 pt tapered Mason glass jar having a 100-mesh screen lid and the bottom covered with a disk of paper towel. Beetles react abnormally on glass as compared with paper. The jar was placed in a randomized position on the first of 4 parallel lines on a laboratory table; the next jar was placed on the next line; etc. A draft of air from a household fan covered the table. The foregoing procedure was repeated for each insecticide. Sprays of all insecticides were agitated and buffered to pH 6. On each of the following 4 days a separate line of jars was infested with 25 beetles per jar from a laboratory culture of infested elm logs in 5 gal lard cans; each day represented 1 of 4 replicates. Moribund and dead beetles were counted after 24 h and data analyzed once in 1977 and twice during 1978.

Elm Bark Beetle Mortality on Lab-Sprayed Bark Chips, 1981

Abstract Suspended from the edge of a horizontally rotating 27 inch bicycle wheel, four 35 mm x 35 mm elm bark chips were sprayed with an insecticide during 1 pass before a compressed air paint spray gun beneath the wheel axle. The gun delivered 2.2 ml/sec and the wheel turned 4 rpm. This apparatus was in the opening of a laboratory evacuation hood. Bark chips, including some sapwood, had been cut with a band saw from 100 mm dia log disks from a recently felled tree. When each sprayed chip was nearly dry it was dropped into a 0.5 pt tapered Mason glass jar having a 100-mesh screen lid and the botton covered with a disk of paper towel. Beetles react abnormally on glass as compared with paper. The jar was placed in a randomized position on the first of 4 parallel lines on a laboratory table; the next jar was placed on the next line; etc. A draft of air from a household fan covered the table. The foregoing procedure was repeated for each insecticide. Sprays of all insecticides were agitated and buffered to pH 6. On each of the following 4 days a separate line of jars was infested with 25 beetles per jar from a laboratory culture of infested elm logs in 5 gal lard cans; each day represented 1 of 4 replicates. Moribund and dead beetles were counted after 24 hr. With poorer treatments this usually involved dissecting the chip to find the boring beetles. Results were subjected to a 2-way analysis of variance.