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Object-based SCM: An Efficient Interface for Storage Class Memories
"... Abstract—Storage Class Memory (SCM) has become increasingly popular in enterprise systems as well as embedded and mobile systems. However, replacing hard drives with SCMs in current storage systems often forces either major changes in file systems or suboptimal performance, because the current block ..."
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Abstract—Storage Class Memory (SCM) has become increasingly popular in enterprise systems as well as embedded and mobile systems. However, replacing hard drives with SCMs in current storage systems often forces either major changes in file systems or suboptimal performance, because the current block-based interface does not deliver enough information to the device to allow it to optimize data management for specific device characteristics such as the out-of-place update. To alleviate this problem and fully utilize different characteristics of SCMs, we propose the use of an object-based model that provides the hardware and firmware the ability to optimize performance for the underlying implementation, and allows drop-in replacement for devices based on new types of SCM. We discuss the design of object-based SCMs and implement an object-based flash memory prototype. By analyzing different design choices for several subsystems, such as data placement policies and index structures, we show that our object-based model provides comparable performance to other flash file systems while enabling advanced features such as object-level reliability. I.
iv TABLE OF CONTENTS
, 2013
"... iii EPIGRAPH Nobody ever figures out what life is all about, and it doesn’t matter. Explore the world. Nearly everything is really interesting if you go into it deeply enough. ..."
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iii EPIGRAPH Nobody ever figures out what life is all about, and it doesn’t matter. Explore the world. Nearly everything is really interesting if you go into it deeply enough.
ANALYSIS OF TRADE-OFFS IN V2P-TABLE DESIGN FOR NAND FLASH
"... Flash memory uses relocate-on-write, also called out-of-place write for performance reasons. Data files from the host are spread across several non-sequential NAND physical pages. In order to retrieve host data at a later point a virtual-tophysical address table mapping the files to their physical a ..."
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Flash memory uses relocate-on-write, also called out-of-place write for performance reasons. Data files from the host are spread across several non-sequential NAND physical pages. In order to retrieve host data at a later point a virtual-tophysical address table mapping the files to their physical addresses must be maintained. This process entails two basic steps. The first is to divide the NAND physical space in a hierarchical manner for efficiency of address lookup. The second is to store the resulting address lookup table, also called a virtual-to-physical (V2P) table in an efficient manner on the flash. This paper explores different architectures for constructing such table and storing it, thereby characterizing the trade-off that they offer in terms of complexity, write speed, and endurance of the flash memory. 1.
Flash Device Support for Database Management
"... While disks have offered a stable behavior for decades-thus guaranteeing the timelessness of many database design decisions, flash devices keep on mutating. Their behavior varies across models and across firmware updates for the same model. Many researchers have proposed to adapt database algorithms ..."
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While disks have offered a stable behavior for decades-thus guaranteeing the timelessness of many database design decisions, flash devices keep on mutating. Their behavior varies across models and across firmware updates for the same model. Many researchers have proposed to adapt database algorithms for existing flash devices; others have tried to capture the performance characteristics of flash devices. However, today, we neither have a reference DBMS design nor a performance model for flash devices: database researchers are running after flash memory technology. In this paper, we take the reverse approach and we define how flash devices should support database management. We advocate that flash devices should provide DBMS with more control over IO behavior without sacrificing correctness or robustness. We introduce the notion of bimodal flash devices that expose the full potential of the underlying flash chips as long as the submitted IOs respect a few well-defined constraints. We suggest two approaches for implementing bimodal flash devices: (a) based on the narrow block device interface, or (b) based on a rich interface that allows a DBMS to explicitly control IO behavior. We believe that these approaches are natural evolutions of the current generation of flash devices, whose complexity and opacity is illsuited for database management. We discuss how bimodal flash devices would benefit many existing techniques proposed by the database research community, and identify a set of new research issues. 1.
reFreshSSDs: EnablingHighEndurance,Low CostFlashin
"... Storageperformanceandpowerarecritical issuesin moderndatacenters. Solid State Drives(SSDs) offer both performance and power advantages over hard disk drives. With the advent of MLC flash, the cost-per-Gigabyte of Flash has dropped significantly enough to make it attractive for use in largescale stor ..."
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Storageperformanceandpowerarecritical issuesin moderndatacenters. Solid State Drives(SSDs) offer both performance and power advantages over hard disk drives. With the advent of MLC flash, the cost-per-Gigabyte of Flash has dropped significantly enough to make it attractive for use in largescale storage in datacenters. However, flash suffers from limited endurance and wears away after a certainnumberofwritesanderases,therebyentailinghigherreplacementandservicecostsandhencean increase in the overallserverinfrastructurecosts. Inthis paper,we developa physically-accuratemodel of flash memory reliability and show that there exists a tradeoff between endurance and retention time. We then quantify this tradeoff and show how to exploit it without causing data integrity problems by refreshingthedataintheflashmemorycells. We proposeandevaluateanEarliest-DeadlineFirst (EDF) basedrefreshpolicythat canincreasethe endurancelimit by6-56%foranMLC-basedSSD. 1
Chronos: a NoSQL System on Flash Memory for Industrial Process Data
"... Abstract Within Électricité de France (EDF) hydroelectric power stations, IGCBoxes are industrial mini PCs dedicated to industrial process data archiv-ing. These equipments expose distinctive features, mainly on their storage sys-tem based exclusively on flash memory due to environmental constraints ..."
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Abstract Within Électricité de France (EDF) hydroelectric power stations, IGCBoxes are industrial mini PCs dedicated to industrial process data archiv-ing. These equipments expose distinctive features, mainly on their storage sys-tem based exclusively on flash memory due to environmental constraints. This type of memory had notable consequences on data acquisition performance, with a substantial drop compared with hard disk drives. In this setting, we have designed Chronos, an open-source NoSQL system for sensor data manage-ment on flash memories. Chronos includes an efficient quasi-sequential write pattern along with an index management technique adapted for process data management. As a result, Chronos supports a higher velocity for inserted data, with acquisition rates improved by a factor of 20 to 54 over different solutions, therefore solving a practical bottleneck for EDF. Keywords database · flash memory · NoSQL system · data historian 1
