11 research outputs found
Node Repair for Distributed Storage Systems over Fading Channels
Distributed storage systems and associated storage codes can efficiently
store a large amount of data while ensuring that data is retrievable in case of
node failure. The study of such systems, particularly the design of storage
codes over finite fields, assumes that the physical channel through which the
nodes communicate is error-free. This is not always the case, for example, in a
wireless storage system.
We study the probability that a subpacket is repaired incorrectly during node
repair in a distributed storage system, in which the nodes communicate over an
AWGN or Rayleigh fading channels. The asymptotic probability (as SNR increases)
that a node is repaired incorrectly is shown to be completely determined by the
repair locality of the DSS and the symbol error rate of the wireless channel.
Lastly, we propose some design criteria for physical layer coding in this
scenario, and use it to compute optimally rotated QAM constellations for use in
wireless distributed storage systems.Comment: To appear in ISITA 201
A Repair Framework for Scalar MDS Codes
Several works have developed vector-linear maximum-distance separable (MDS)
storage codes that min- imize the total communication cost required to repair a
single coded symbol after an erasure, referred to as repair bandwidth (BW).
Vector codes allow communicating fewer sub-symbols per node, instead of the
entire content. This allows non trivial savings in repair BW. In sharp
contrast, classic codes, like Reed- Solomon (RS), used in current storage
systems, are deemed to suffer from naive repair, i.e. downloading the entire
stored message to repair one failed node. This mainly happens because they are
scalar-linear. In this work, we present a simple framework that treats scalar
codes as vector-linear. In some cases, this allows significant savings in
repair BW. We show that vectorized scalar codes exhibit properties that
simplify the design of repair schemes. Our framework can be seen as a finite
field analogue of real interference alignment. Using our simplified framework,
we design a scheme that we call clique-repair which provably identifies the
best linear repair strategy for any scalar 2-parity MDS code, under some
conditions on the sub-field chosen for vectorization. We specify optimal repair
schemes for specific (5,3)- and (6,4)-Reed- Solomon (RS) codes. Further, we
present a repair strategy for the RS code currently deployed in the Facebook
Analytics Hadoop cluster that leads to 20% of repair BW savings over naive
repair which is the repair scheme currently used for this code.Comment: 10 Pages; accepted to IEEE JSAC -Distributed Storage 201
Alpha Entanglement Codes: Practical Erasure Codes to Archive Data in Unreliable Environments
Data centres that use consumer-grade disks drives and distributed
peer-to-peer systems are unreliable environments to archive data without enough
redundancy. Most redundancy schemes are not completely effective for providing
high availability, durability and integrity in the long-term. We propose alpha
entanglement codes, a mechanism that creates a virtual layer of highly
interconnected storage devices to propagate redundant information across a
large scale storage system. Our motivation is to design flexible and practical
erasure codes with high fault-tolerance to improve data durability and
availability even in catastrophic scenarios. By flexible and practical, we mean
code settings that can be adapted to future requirements and practical
implementations with reasonable trade-offs between security, resource usage and
performance. The codes have three parameters. Alpha increases storage overhead
linearly but increases the possible paths to recover data exponentially. Two
other parameters increase fault-tolerance even further without the need of
additional storage. As a result, an entangled storage system can provide high
availability, durability and offer additional integrity: it is more difficult
to modify data undetectably. We evaluate how several redundancy schemes perform
in unreliable environments and show that alpha entanglement codes are flexible
and practical codes. Remarkably, they excel at code locality, hence, they
reduce repair costs and become less dependent on storage locations with poor
availability. Our solution outperforms Reed-Solomon codes in many disaster
recovery scenarios.Comment: The publication has 12 pages and 13 figures. This work was partially
supported by Swiss National Science Foundation SNSF Doc.Mobility 162014, 2018
48th Annual IEEE/IFIP International Conference on Dependable Systems and
Networks (DSN
Sparsity Exploiting Erasure Coding for Resilient Storage and Efficient I/O Access in Delta based Versioning Systems
In this paper we study the problem of storing reliably an archive of
versioned data. Specifically, we focus on systems where the differences
(deltas) between subsequent versions rather than the whole objects are stored -
a typical model for storing versioned data. For reliability, we propose erasure
encoding techniques that exploit the sparsity of information in the deltas
while storing them reliably in a distributed back-end storage system, resulting
in improved I/O read performance to retrieve the whole versioned archive. Along
with the basic techniques, we propose a few optimization heuristics, and
evaluate the techniques' efficacy analytically and with numerical simulations.Comment: 10 pages, 8 figure
Secure Cooperative Regenerating Codes for Distributed Storage Systems
Regenerating codes enable trading off repair bandwidth for storage in
distributed storage systems (DSS). Due to their distributed nature, these
systems are intrinsically susceptible to attacks, and they may also be subject
to multiple simultaneous node failures. Cooperative regenerating codes allow
bandwidth efficient repair of multiple simultaneous node failures. This paper
analyzes storage systems that employ cooperative regenerating codes that are
robust to (passive) eavesdroppers. The analysis is divided into two parts,
studying both minimum bandwidth and minimum storage cooperative regenerating
scenarios. First, the secrecy capacity for minimum bandwidth cooperative
regenerating codes is characterized. Second, for minimum storage cooperative
regenerating codes, a secure file size upper bound and achievability results
are provided. These results establish the secrecy capacity for the minimum
storage scenario for certain special cases. In all scenarios, the achievability
results correspond to exact repair, and secure file size upper bounds are
obtained using min-cut analyses over a suitable secrecy graph representation of
DSS. The main achievability argument is based on an appropriate pre-coding of
the data to eliminate the information leakage to the eavesdropper
Hadoop : processament distribuït de gran volum de dades en el núvol d'Apache
Avui en dia es genera un volum increïble de dades de diferents tipus i que provenen de multitud d'orÃgens. Els sistemes d'emmagatzematge i processament distribuït són els elements tecnològics que fan possible capturar aquest allau de dades i permeten donar-ne un valor a través d'anà lisis diversos. Hadoop, que integra un sistema d'emmagatzematge i processament distribuïts, s'ha convertit en l'està ndard de-facto per a aplicacions que necessiten una gran capacitat d'emmagatzematge, inclús de l'ordre de desenes de PBs. En aquest treball farem un estudi de Hadoop, analitzarem l'eficiència del seu sistema de durabilitat i en proposarem una alternativa.Hoy en dÃa se genera un volumen increÃble de datos de diferentes tipos y que proceden de multitud de orÃgenes. Los sistemas de almacenamiento y procesado distribuidos son los elementos tecnológicos que hacen posible capturar esta avalancha de datos y permiten extraer un valor de ellos a través de diferentes tipos de análisis. Hadoop, que integra un sistema de almacenaje y procesado distribuidos, se ha convertido en el estándar de-facto para aplicaciones que necesitan una gran capacidad de almacenaje, incluso del orden de decenas de PBs. En el presente trabajo realizaremos un estudio de Hadoop, analizaremos la eficiencia de su sistema de durabilidad, y propondremos una alternativa.Nowadays, the amount of data generated, which comes from various sources, is overwhelming. Distributed storage systems are the technological solution that make possible to capture this avalanche of data and to obtain a value from it. Hadoop, which offers a distributed storage and processing systems, has become the de-facto standard for applications that seek for a big storage capacity, even in the order of tens of PBs. In the present work, we'll study Hadoop, we'll analyze its durability system's efficiency and we will propose an alternative to it