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<p class="MsoNormal">That comment in the Administration guide is a legacy comment when Metadata sub-block size was restricted to 1/32 of the Metadata block size. In the past, creating large Metadata block sizes also meant large sub-blocks and hence large directory
blocks which wasted a lot of space.<o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black"><gpfsug-discuss-bounces@spectrumscale.org> on behalf of "Buterbaugh, Kevin L" <Kevin.Buterbaugh@Vanderbilt.Edu><br>
<b>Reply-To: </b>gpfsug main discussion list <gpfsug-discuss@spectrumscale.org><br>
<b>Date: </b>Monday, August 6, 2018 at 11:37 AM<br>
<b>To: </b>gpfsug main discussion list <gpfsug-discuss@spectrumscale.org><br>
<b>Subject: </b>Re: [gpfsug-discuss] Sub-block size not quite as expected on GPFS 5 filesystem?<o:p></o:p></span></p>
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<p class="MsoNormal"><a name="_MailOriginalBody">Hi All, <o:p></o:p></a></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">So I was just reading the GPFS 5.0.0 Administration Guide (yes, I actually do look at the documentation even if it seems sometimes that I don’t!) for some other information and happened to come
across this at the bottom of page 358:<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:10.0pt;font-family:Palatino">The
<b>--metadata-block-size </b>flag on the <b>mmcrfs </b>command can be used to create a system pool with a different block size from the user pools. This can be especially beneficial if the default block size is larger than 1 MB. If data and metadata block sizes
differ, the system pool must contain only <b>metadataOnly </b>disks. </span><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Given that one of the responses I received during this e-mail thread was from an IBM engineer basically pointing out that there is no benefit in setting the metadata-block-size to less than 4
MB if that’s what I want for the filesystem block size, this might be a candidate for a documentation update.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Thanks…<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Kevin<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">—<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Kevin Buterbaugh - Senior System Administrator<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Vanderbilt University - Advanced Computing Center for Research and Education<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"></span><a href="mailto:Kevin.Buterbaugh@vanderbilt.edu"><span style="mso-bookmark:_MailOriginalBody">Kevin.Buterbaugh@vanderbilt.edu</span><span style="mso-bookmark:_MailOriginalBody"></span></a><span style="mso-bookmark:_MailOriginalBody"> -
(615)875-9633<o:p></o:p></span></p>
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