snapraid/design.html

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<meta name="description" content="A backup program for disk arrays. It stores parity information of your data and it recovers from up to six disk failures" />
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<meta name="author" content="Andrea Mazzoleni" />
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<p>
<span class="bold">SnapRAID</span> was created following the <a href="http://en.wikipedia.org/wiki/Unix_philosophy">Unix philosophy</a>:
<em>Write programs that do one thing and do it well</em>.
</p>

<p>
The first design principle was <span class="bold">reliability</span>.
The result is a simple architecture and an easy to understand implementation,
following the <a href="http://en.wikipedia.org/wiki/Edsger_W._Dijkstra">Dijkstra</a>
quote <i>Simplicity is prerequisite for reliability</i>.
</p>
<p>
Extensive and automated tests with the runtime checker <a href="http://valgrind.org/">valgrind</a> and
the static analyzer <a href="http://clang-analyzer.llvm.org/">clang</a> are done to ensure the correctness of the final application.
The test has a <a href="cov/">code coverage of over 90%</a>, measured with <a href="http://ltp.sourceforge.net/coverage/lcov.php">lcov</a>.
</p>

<p>
The second design principle was <span class="bold">robustness</span>.
It supports any kind of problem. Even on kernel panics, power-downs
or any other hard failure at runtime, your redundancy data is in safe hands.
<br>
It uses all the possible storage techniques to ensure to always keep consistent
redundancy even after critical interruptions.
</p>

<p>
The third design principle was <span class="bold">efficiency</span>.
It's a native C application highly optimized using all the
possible OS services to ensure the maximum throughput of you disk array.
</p>
<p>
For integrity checks is used the highly efficient <a href="http://code.google.com/p/smhasher/">murmur3</a>
and <a href="http://burtleburtle.net/bob/hash/spooky.html">SpookyHash</a> hashes at 128 bits.
For the redundancy computations we use a
<a href="https://github.com/amadvance/snapraid/tree/master/raid">RAID library</a>
written from scratch that supports up to six levels of parity delivering top-notch performance.
The library design is originally based, and also binary compatible,
with the <a href="http://lxr.linux.no/linux+*/lib/raid6">Linux Kernel RAID</a>
library made by H. Peter Anvin.
As internal data base it's used the <a href="http://www.tommyds.it/">TommyDS</a> library of data structures.
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