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<span id="ft-data-reliability-label"></span><h1><span class="section-number">11.6.3. </span>End-to-end data reliability for MPI messages<a class="headerlink" href="#end-to-end-data-reliability-for-mpi-messages" title="Permalink to this heading"></a></h1>
<p>Current Open MPI releases have no support for end-to-end data
reliability, at least not more than currently provided by the
underlying network.</p>
<p>Previous releases included a data reliability PML component (<code class="docutils literal notranslate"><span class="pre">dr</span></code>) that
assumed that the underlying
network is unreliable. It could drop / restart connections, retransmit
corrupted or lost data, etc. The end effect was that data sent through MPI API
functions would be guaranteed to be reliable.</p>
<p>For example, if you’re using TCP as a message transport, chances of
data corruption are fairly low. However, other interconnects do <em>not</em>
guarantee that data will be uncorrupted when traveling across the
network. Additionally, there are non-zero possibilities that data can
be corrupted while traversing PCI buses, etc. (some corruption errors
at this level can be caught/fixed, others cannot). Such errors are
not uncommon at high altitudes (!).</p>
<p>Note that such added reliability does incur a performance cost —
latency and bandwidth suffer when Open MPI performs the consistency
checks that are necessary to provide such guarantees.</p>
<p>Most clusters/networks do not need data reliability. But some do
(e.g., those operating at high altitudes). The <code class="docutils literal notranslate"><span class="pre">dr</span></code> PML was intended for
these rare environments where reliability was an issue; and users were
willing to tolerate slightly slower applications in order to guarantee
that their job does not crash (or worse, produce wrong answers).</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">dr</span></code> component has been removed from current releases
of Open MPI, but is still available in older releases.</p>
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