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Generalized Expanded-Blaum-Roth (GEBR) codes [1] are designed for large-scale distributed storage systems that have larger recoverability for single-symbol failures, multi-column failures and multi-row failures, compared with locally recoverable codes (LRC). GEBR codes encode an $\alpha\times k$ information array into a $p\tau\times (k+r)$ array such that lines of slope $i$ with $0\leq i\leq r-1$ have even parity and each column contains $p\tau-\alpha$ local parity symbols, where $p$ is an odd prime and $k+r\leq p\tau$. Necessary and sufficient conditions for GEBR codes to be $(n,k)$ recoverable (i.e., any $k$ out of $n=k+r$ columns can retrieve all information symbols) are given in [2] for $\alpha=(p-1)\tau$. However, the $(n,k)$ recoverable condition of GEBR codes is unknown when $\alpha<(p-1)\tau$. In this paper, we present the $(n,k)$ recoverable condition for GEBR codes for $\alpha< (p-1)\tau$. In addition, we present a sufficient condition for enabling GEBR codes to recover some erased lines of any slope $i$ ($0\leq i\leq p\tau-1$) for any parameter $r$ when $\tau$ is a power of $p$. Moreover, we present the construction of Generalized Blaum-Roth (GBR) codes that encode an $\alpha\times k$ information array into an $\alpha\times (k+r)$ array. We show that GBR codes share the same MDS condition as the $(n,k)$ recoverable condition of GEBR codes, and we also present a sufficient condition for GBR codes to recover some erased lines of any slope $i$ ($0\leq i\leq \alpha-1$).

A maximum distance separable (MDS) array code is composed of $m\times (k+r)$ arrays such that any $k$ out of $k+r$ columns suffice to retrieve all the information symbols. Expanded-Blaum-Roth (EBR) codes and Expanded-Independent-Parity (EIP) codes are two classes of MDS array codes that can repair any one symbol in a column by locally accessing some other symbols within the column, where the number of symbols $m$ in a column is a prime number. By generalizing the constructions of EBR and EIP codes, we propose new MDS array codes, such that any one symbol can be locally recovered and the number of symbols in a column can be not only a prime number but also a power of an odd prime number. Also, we present an efficient encoding/decoding method for the proposed generalized EBR (GEBR) and generalized EIP (GEIP) codes based on the LU factorization of a Vandermonde matrix. We show that the proposed decoding method has less computational complexity than existing methods. Furthermore, we show that the proposed GEBR codes have both a larger minimum symbol distance and a larger recovery ability of erased lines for some parameters when compared to EBR codes. We show that EBR codes can recover any $r$ erased lines of a slope for any parameter $r$, which was an open problem in [2].

The Shamir secret sharing scheme requires a Maximum Distance Separable (MDS) code, and in its most common implementation, a Reed-Solomon (RS) code is used. In this paper, we observe that the encoding procedure can be made simpler and faster by dropping the MDS condition and specifying the possible symbols that can be shared. In particular, the process can be made even faster by using array codes based on XOR operations instead of RS codes.

Expanded Blaum-Roth (EBR) codes consist of $n\times n$ arrays such that lines of slopes $i$, $0\leq i\leq r-1$ for $2\leq r

The traditional definition of Integrated Interleaved (II) codes generally assumes that the component nested codes are either Reed-Solomon (RS) or shortened Reed-Solomon codes. By taking general classes of codes, we present a recursive construction of Extended Integrated Interleaved (EII) codes into multiple layers, a problem that brought attention in literature for II codes. The multiple layer approach allows for a hierarchical scheme where each layer of the code provides for a different locality. In particular, we present the erasure-correcting capability of the new codes and we show that they are ideally suited as Locally Recoverable (LRC) codes due to their hierarchical locality and the small finite field required by the construction. Properties of the multiple layer EII codes, like their minimum distance and dimension, as well as their erasure decoding algorithms, parity-check matrices and performance analysis, are provided and illustrated with examples. Finally, we will observe that the parity-check matrices of high layer EII codes have low density., Comment: 21 pages, 1 table

When digital data are transmitted over a noisy channel, it is important to have a mechanism allowing recovery against a limited number of errors. Normally, a user string of 0's and 1's, called bits, is encoded by adding a number of redundant bits to it. When the receiver attempts to reconstruct the original message sent, it starts by examining a possibly corrupted version of the encoded message, and then makes a decision. This process is called the decoding. The purpose of this course is giving an introduction to the theory and practice of error-correcting codes.

In general, array codes consist of $m\times n$ arrays and in many cases, the arrays satisfy parity constraints along lines of different slopes (generally with a toroidal topology). Such codes are useful for RAID type of architectures, since they allow to replace finite field operations by XORs. We present expansions to traditional array codes of this type, like Blaum-Roth (BR) and extended EVENODD codes, by adding parity on columns. This vertical parity allows for recovery of one or more symbols in a column locally, i.e., by using the remaining symbols in the column without invoking the rest of the array. Properties and applications of the new codes are discussed, in particular to Locally Recoverable (LRC) codes.

Integrated Interleaved (II) and Extended Integrated Interleaved (EII) codes are a versatile alternative for Locally Recoverable (LRC) codes, since they require fields of relatively small size. II and EII codes are generally defined over Reed-Solomon type of codes. A new comprehensive definition of EII codes is presented, allowing for EII codes over any field, and in particular, over the binary field $GF(2)$. The traditional definition of II and EII codes is shown to be a special case of the new definition. Improvements over previous constructions of LRC codes, in particular, for binary codes, are given, as well as cases meeting an upper bound on the minimum distance. Properties of the codes are presented as well, in particular, an iterative decoding algorithm on rows and columns generalizing the iterative decoding algorithm of product codes. Two applications are also discussed: one is finding a systematic encoding of EII codes such that the parity symbols have a balanced distribution on rows, and the other is the problem of ordering the symbols of an EII code such that the maximum length of a correctable burst is achieved., Comment: 25 pages

A new class of codes, Extended Product (EPC) Codes, consisting of a product code with a number of extra parities added, is presented and applications for erasure decoding are discussed. An upper bound on the minimum distance of EPC codes is given, as well as constructions meeting the bound for some relevant cases. A special case of EPC codes, Extended Integrated Interleaved (EII) codes, which naturally unify Integrated Interleaved (II) codes and product codes, is defined and studied in detail. It is shown that EII codes often improve the minimum distance of II codes with the same rate, and they enhance the decoding algorithm by allowing decoding on columns as well as on rows. It is also shown that EII codes allow for encoding II codes with an uniform distribution of the parity symbols., Comment: 24 pages. arXiv admin note: text overlap with arXiv:1610.04273

Generalized Product (GPC) Codes, an unification of Product Codes and Integrated Interleaved (II) Codes, are presented. Applications for approaches requiring local and global parities are described. The more general problem of extending product codes by adding global parities is studied and an upper bound on the minimum distance of such codes is obtained. Codes with one, two and three global parities whose minimum distances meet the bound are presented. Tradeoffs between optimality and field size are discussed., Comment: 37 pages

Considerable interest has been paid in recent literature to codes combining local and global properties for erasure correction. Applications are in cloud type of implementations, in which fast recovery of a failed storage device is important, but additional protection is required in order to avoid data loss, and in RAID type of architectures, in which total device failures coexist with silent failures at the page or sector level in each device. Existing solutions to these problems require in general relatively large finite fields. The techniques of Integrated Interleaved Codes (which are closely related to Generalized Concatenated Codes) are proposed to reduce significantly the size of the finite field, and it is shown that when the parameters of these codes are judiciously chosen, their performance may be competitive with the one of codes optimizing the minimum distance., Comment: 24 pages, 5 figures and 3 tables

We present simple constructions of optimal erasure-correcting LRC codes by exhibiting their parity-check matrices. When the number of local parities in a parity group plus the number of global parities is smaller than the size of the parity group, the constructed codes are optimal with a field of size at least the length of the code. We can reduce the size of the field to at least the size of the parity groups when the number of global parities equals the number of local parities in a parity group plus one., Comment: 11 pages, 2 figures

Generalized Concatenated (GC), also known as Integrated Interleaved (II) Codes, are studied from an erasure correction point of view making them useful for Redundant Arrays of Independent Disks (RAID) types of architectures combining global and local properties. The fundamental erasure-correcting properties of the codes are proven and efficient encoding and decoding algorithms are provided. Although less powerful than the recently developed PMDS codes, this implementation has the advantage of allowing generalization to any range of parameters while the size of the field is much smaller than the one required for PMDS codes.

Partial MDS (PMDS) codes are erasure codes combining local (row) correction with global additional correction of entries, while Sector-Disk (SD) codes are erasure codes that address the mixed failure mode of current RAID systems. It has been an open problem to construct general codes that have the PMDS and the SD properties, and previous work has relied on Monte-Carlo searches. In this paper, we present a general construction that addresses the case of any number of failed disks and in addition, two erased sectors. The construction requires a modest field size. This result generalizes previous constructions extending RAID~5 and RAID~6.

SD codes are erasure codes that address the mixed failure mode of current RAID systems. Rather than dedicate entire disks to erasure coding, as done in RAID-5, RAID-6 and Reed-Solomon coding, an SD code dedicates entire disks, plus individual sectors to erasure coding. The code then tolerates combinations of disk and sector errors, rather than solely disk errors. It is been an open problem to construct general codes that have the SD property, and previous work has relied on Monte Carlo searches. In this paper, we present two general constructions that address the cases with one disk and two sectors, and two disks and two sectors. Additionally, we make an observation about shortening SD codes that allows us to prune Monte Carlo searches., Comment: 8 pages. arXiv admin note: text overlap with arXiv:1305.0032

A construction of Partial Maximum Distance Separable (PMDS) and Sector-Disk (SD) codes extending RAID 5 with two extra parities is given, solving an open problem. Previous constructions relied on computer searches, while our constructions provide a theoretical solution to the problem., Comment: 7 pages

A family of codes with a natural two-dimensional structure is presented, inspired by an application of RAID type of architectures whose units are solid state drives (SSDs). Arrays of SSDs behave differently to arrays of hard disk drives (HDDs), since hard errors in sectors are common and traditional RAID approaches (like RAID 5 or RAID 6) may be either insufficient or excessive. An efficient solution to this problem is given by the new codes presented, called partial-MDS (PMDS) codes., Comment: This new version corrects a typo in Theorem 5.5

In a previous work it was shown that the best measure for the efficiency of a single burst-correcting code is obtained using the Gallager bound as opposed to the Reiger bound. In this paper, an efficient algorithm that searches for the best (shortened) cyclic burst-correcting codes is presented. Using this algorithm, extensive tables that either tie existing constructions or improve them are obtained for burst lengths up to b=10.

Given $r\geq 3$ and $2^{r-1}+1\leq n< 2^{r}-1$, an $[n,n-r,3]$ shortened Hamming code that can detect a maximal number of double errors is constructed. The optimality of the construction is proven., Comment: We withdraw the paper since we found a reference from 1981 that solves exactly the same problem