pyeclib 0.1.10

This library provides a simple Python interface for implementing erasure codes. To obtain the best possible performance, the underlying erasure code algorithms are written in C.

This is v0.1 of PyECLib. This library provides a simple Python interface for implementing erasure codes. To obtain the best possible performance, the underlying erasure code algorithms are written in C. Please let me know if you have any other issues building/installing (email: [e-mail]).

This library makes use of Jerasure for Reed-Solomon and provides its own flat XOR-based erasure code encoder and decoder. Currently, it implements a specific class of HD Combination Codes (see “Flat XOR-based erasure codes in storage systems: Constructions, efficient recovery, and tradeoffs” in IEEE MSST 2010). These codes are well-suited to archival use-cases, have a simple construction and require a minimum number of participating disks during single-disk reconstruction (think XOR-based LRC code).

The XOR-based codes make use of 128-bit registers using the Intel SIMD extensions. We are currently working on incorporating GF-Complete into Jerasure. Version 1.0 of this library will link to a new version of Jerasure that uses the Intel SIMD instruction set for Vandermonde Reed-Solomon encoding (see GF-Complete 1.0: http://web.eecs.utk.edu/~plank/plank/papers/CS-13-703.html and “Screaming fast Galois Field arithmetic using Intel SIMD instructions” in USENIX FAST 2013).

Examples of using this library are provided in ./tools:

Command-line encoder: ec_pyeclib_encode.py

Command-line decoder: ec_pyeclib_decode.py

Utility to determine what is needed to reconstruct missing fragments: pyeclib_fragments_needed.py

The main Python interface only contains 6 functions:

Encode N bytes into k+m fragments (returns list of fragments):

def encode(self, bytes)

Decode between k and k+m fragments into a string (returns a string):

def decode(self, fragment_payloads)

Reconstruct “missing_fragment_indexes” using “available_fragment_payloads”:

def reconstruct(self, available_fragment_payloads, missing_fragment_indexes)

Return the indexes of fragments needed to reconstruct “missing_fragment_indexes”:

def fragments_needed(self, missing_fragment_indexes)

Return an opaque buffer known by the underlying library:

def get_metadata(self, fragment)

Use opaque buffers from get_metadata() to verify a the consistency of a stripe:

def verify_stripe_metadata(self, fragment_metadata_list)

Quick Start:

Standard stuff to install: Python 2.7 (including devel), argparse

If you do not have Jerasure installed. Install it from the unofficial GitHub repo linked from here (setup.py assumes it will be in /usr/local):

https://bitbucket.org/kmgreen2/jerasure-kmg

This version of Jerasure is a development version that includes SIMD support using GF-Complete. You will also need to install GF-Complete:

https://bitbucket.org/jimplank/gf-complete

GF-Complete does not have an ‘install’ target, so either put an install target into the makefile, or

1.) cp gf_complete.a /usr/local/lib/libgf_complete.a 2.) cp gf_complete.h /usr/local/include

Alternatively, you can install my fork of gf-complete, which includes an install:

https://bitbucket.org/kmgreen2/gf-complete-kmg

Install PyECLib:

sudo python setup.py install

Run the test suite:

cd test; python run_tests.py; ./ec_pyeclib_file_test.sh; cd ..

If all of this works, then you should be good to go. If not, send me an email!

If the test suite fails because it cannot find any of the shared libraries, then you probably need to add /usr/local/lib to the path searched when loading libraries. The best way to do this (on Linux) is to add ‘/usr/local/lib’ to

/etc/ld.so.conf

and then run:

ldconfig