leo_erasure

Overview

• "leo_erasure" is a Erlang binding for the open sourced Erasure Coding library "Jerasure"
  • Coding Supported: Reed-Solomon Code (Vandermonde/Cauchy), Liberation Code
• "leo_erasure" uses rebar build system. Makefile so that simply running "make" at the top level should work.

Description

• Object would be encoded into {k + m} blocks, any {k} blocks could be used to decode back
• K: The number of data chunks - The number of chunks in which the original object is divided
• M: The number of coding chunks - The number of additional chunks computed by leo_erasure's encoding functions

Dependencies

• Erlang 16/17
• Automake 1.13+, Autoconf 2.65+ and Libtool

Installation

For Ubuntu 14.04LTS or higher

$ sudo apt-get install git automake autoconf libtool build-essential yasm

For RHEL/CentOS v6/7

## ------------------------------
## For CentOS/RHEL 6.5/6.6 and 7
## ------------------------------
## 1. You need to install ``autoconf`` because Leo's erasure-coding lib requires Autoconf 2.69 or higher
$ cd <workspace>/
$ wget http://ftp.gnu.org/gnu/autoconf/autoconf-2.69.tar.gz
$ tar xvfvz autoconf-2.69.tar.gz
$ cd autoconf-2.69
$ ./configure && make && sudo make install
$ autoconf --version
autoconf (GNU Autoconf) 2.69
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>, <http://gnu.org/licenses/exceptions.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David J. MacKenzie and Akim Demaille.

## 2. Furthermore, according to the same reason of ``autoconf``, you need to install the latest ``automake`` manually.
$ cd <workspace>/
$ wget http://ftp.gnu.org/gnu/automake/automake-1.14.1.tar.gz
$ tar xzf automake-1.14.1.tar.gz
$ cd automake-1.14.1
$ ./configure && make && sudo make install
$ automake --version
automake (GNU automake) 1.14.1
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl-2.0.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Tom Tromey <tromey@redhat.com>
       and Alexandre Duret-Lutz <adl@gnu.org>.

## 3. ISA-L uses YASM, you need to install yasm >1.2.0
$ cd <workspace>/
$ wget http://www.tortall.net/projects/yasm/releases/yasm-1.2.0.tar.gz
$ tar xzf yasm-1.2.0.tar.gz
$ cd yasm-1.2.0
$ ./configure && make && sudo make install
$ yasm --version
yasm 1.2.0
Compiled on Oct 10 2013.
Copyright (c) 2001-2011 Peter Johnson and other Yasm developers.
Run yasm --license for licensing overview and summary.

Data Types

coding_class()

• coding_class() = vandrs | cauchyrs | liberation
  • vandrs (default) - Vandermonde-based Reed-Solomon codes which is based on traditional Reed-Solomon codes
  • cauchyrs - Cauchy-based Reed-Solomon codes which is also based on traditional Reed-Solomon codes
  • liberation - Liberation coding and decoding are based on a bit matrix-vector product very similar to the those used in Reed-Solomon coding and Cauchy Reed-Solomon coding

id_with_block()

• id_with_block() = {non_neg_integer(), binary()}

Exports

Encoding an object

Encode an object with leo_erasure's encoding functions

encode/2

encode({CodingParam_K, CodingParam_M}, Bin) ->
    {ok, IdWithBlockL}|{error, Cause}

• Types
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • Bin = binary()
  • IdWithBlockL = [id_with_block()]
  • Cause = any()

encode/3

encode(CodingClass, CodingParams, Bin) ->
    {ok, IdWithBlockL}|{error, Cause}

• Types
  • CodingClass = coding_class()
  • CodingParams = {CodingParam_K, CodingParam_M, CodingParam_W}
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • CodingParam_W = pos_integer()
  • Bin = binary()
  • IdWithBlockL = [id_with_block()]
  • Cause = any()

Decoding an object

Decode an object with leo_erasure's decoding functions

decode/3

decode({CodingParam_K, CodingParam_M}, IdWithBlockL, ObjSize) ->
    {ok, Bin}|{error, Cause}

• Types
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • IdWithBlockL = [id_with_block()]
  • ObjSize = pos_integer()
  • Bin = binary()
  • Cause = any()

decode/4

decode(CodingClass, CodingParams, IdWithBlockL, ObjSize) ->
    {ok, Bin}|{error, Cause}

• Types
  • CodingClass = coding_class()
  • CodingParams = {CodingParam_K, CodingParam_M, CodingParam_W}
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • CodingParam_W = pos_integer()
  • IdWithBlockL = [id_with_block()]
  • ObjSize = pos_integer()
  • Bin = binary()
  • Cause = any()

Repairing multi blocks

Repair multiple blocks to retain complete blocks of the object

repair/3

repair({CodingParam_K, CodingParam_M}, IdWithBlockL) ->
    {ok, IdWithBlockL} | {error, any()}

• Types
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • IdWithBlockL = [id_with_block()]
  • Cause = any()

repair/4

repair(CodingClass, CodingParams, IdWithBlockL) ->
    {ok, IdWithBlockL} | {error, any()}

• Types
  • CodingClass = coding_class()
  • CodingParams = {CodingParam_K, CodingParam_M, CodingParam_W}
  • CodingParam_K = pos_integer()
  • CodingParam_M = pos_integer()
  • CodingParam_W = pos_integer()
  • IdWithBlockL = [id_with_block()]
  • Cause = any()

Notes

• Stack Size Related Discussion
  • After 0.6.0, temporary structures such as decoding schedules are stored in stack, it would take ~10*k*k*w*w*(size of int) for each instance with Cauchy-RS or Liberation Code. Pratically, using paramters w=8, k=20, m<k with Cauchy-RS would consume ~1MB

Sponsors

LeoProject/LeoFS is sponsored by Rakuten, Inc. and supported by Rakuten Institute of Technology.