<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial">On Fri, Feb 28, 2014 at 12:07 PM, Ravishankar N </span><span dir="ltr" style="font-family:arial"><<a href="mailto:ravishankar@redhat.com" target="_blank">ravishankar@redhat.com</a>></span><span style="font-family:arial"> wrote:</span><br>
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<div>On 02/28/2014 07:28 AM, Zhang Huan
wrote:<br>
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<div style="font-family:arial,helvetica,sans-serif">Hello <span style="font-family:arial,sans-serif;font-size:13px">Ravi,</span></div>
<div style="font-family:arial,helvetica,sans-serif">
<span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div>
<div style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,sans-serif;font-size:13px">Thanks
for your reply.</span></div>
<div style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div>
<div style="font-family:arial,helvetica,sans-serif">
<span style="font-family:arial,sans-serif;font-size:13px">Sorry
that I have a typo in my mail. It should by "underlying
corruption" instead of "underlying correction".</span></div>
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<br>
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<div><font face="arial, sans-serif">I
guess the logic of eliminating zero byte files from all
innocent nodes is working for preventing underlying
corruption to propagate to other brick. Asked in another
way, if the underlying brick finds some file is corrupted,
anything it could do to tell glusterfs to fix it?</font></div>
<div style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,sans-serif;font-size:13px"><br>
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Hi Zhang,<br>
If all nodes are innocent (from AFR's point of view) ,then AFR
cannot use the changelog attributes to determine which is source.
In this case, the safest bet is to mark all zero byte files as sink,
so that we don't end up healing in the wrong direction. Like I said
earlier, AFR can only use the changelog attributes (xattrs) to
determine the source/sinks. It cannot detect underlying on disk file
system corruptions outside the scope of the xattrs. <br>
<br>
If you are sure that a particular brick is the right source despite
the xattrs saying otherwise, you can manually change the attributes
of the file on all bricks so that AFR now sees that brick as the
source and heals in the expected direction.<br>
<br>
-Ravi</div></blockquote><div><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Hello Ravi,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">
IMO, changing the attributes might be dangerous, since concurrent access with glusterfs is introduced. Not sure if glusterfs has already provided some mechanism for this.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">
<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">My suggestion is to eliminate the zero-byte file from heal source even if is marked as a source. If the underlying filesystem finds some corruption (by scrubbing daemon after checking data checksum), it could truncate it to 0 and let glusterfs to do the healing job. Here is several cases of analysis in my mind.</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">1. If this corrupted file is marked as the only source, then there is no correct replica in the filesystem (actually all are fools), just pick any one as the source to heal is OK;</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">2. If the corrupted file is one of the potential sources, eliminate this one should keep healing in the right direction without further corrupting other correct replicas.</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">3. If the corrupted file is not marked as a source, some other replica will be chosen as a source and this file will be overwritten with correct data.</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">4. If there is no one is marked as clean by attribute, it is quite unlikely this file is chosen as a source as its size is 0. Even it is chosen as a source, there is no further corruption of file content after heal.</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">
<div style="font-family:arial">Zhang Huan</div><div style="font-family:arial"><br></div></div></div></div></div>