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<p class=MsoNormal>I have a bit of a caching issue I was hoping I could get
some help with. Let me start off with a quick synopsis of our currently
installed Lustre system.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>3 Sun x4500s running RHEL4.5 with Lustre 1.6.5. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Most clients run patchless kernels with version 1.6.5 of the
client.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The data this came from was a client with the patched kernel
running version 1.6.7.1.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>All data is served over gigabit connections and in the case
of the x4500s they are serving via 3 bonded GigE connections.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Nightly we run our backups starting at 8pm. Within the
next hour to 3 hours we see the following behavior. A client that was
happily reading along around 4 to 5MB sec will suddenly start reading around 20
MB per second and the packet rate skyrockets at this time too. At this
point the application is reading about a tenth to a fifteenth as slow as
previous rates. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Using the tool collect I have noticed some interesting statistics:<o:p></o:p></p>
<p class=MsoNormal>The lustre reads drop in a similar proportion to the
application performance<o:p></o:p></p>
<p class=MsoNormal>The readahead cache hits quadruple or more<o:p></o:p></p>
<p class=MsoNormal>The readahead cache discards go from 0 to over 1500<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Once the application enters this state it stays in such a
pattern. Killing the job and restarting gives us normal operation. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I am attaching the performance data from a large time
period. The specific event starts at 20:13:36 and ends about 1.5 hours
afterward. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Please let me know if there is something I can tune on the
client to change this behavior or if the backup process will spike this
behavior constantly.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks,<o:p></o:p></p>
<p class=MsoNormal> Dan Kulinski<o:p></o:p></p>
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