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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">This is not totally correct.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">First, LLOG is the underlying technology used to store and handle Lustre Changelogs. But LLOG is used for other Lustre mechanisms, like lustre configuration.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Second, Changelog is similar to an audit feature. Changelog only logs different filesystem change, mostly metadata change, but definitely not the file content change. They don't play
a role at all in transaction or failure recovery. This is only an admin feature.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">At the end, indeed ZIL cannot be used and Lustre has its own mechanisms to guarantee transaction are committed to disk and handle crash. Basicly, I/O are not acknowledge to Lustre clients
before the data is actually on disk. In case of server crash, the Lustre client will replay all non-acknowledge I/Os to ensure none of them are lost.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Changelog is not needed in your case.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Aurélien<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><b><span style="font-size:12.0pt;color:black">De :
</span></b><span style="font-size:12.0pt;color:black">lustre-devel <lustre-devel-bounces@lists.lustre.org> au nom de Sudheendra Sampath <sudheendra.sampath@gmail.com><br>
<b>Date : </b>jeudi 28 janvier 2021 à 21:43<br>
<b>À : </b>"lustre-devel@lists.lustre.org" <lustre-devel@lists.lustre.org><br>
<b>Objet : </b>[EXTERNAL] [lustre-devel] Lustre log question(s)<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><o:p> </o:p></p>
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<p><strong><span style="font-family:"Calibri",sans-serif;color:black;background:#FFFF99">CAUTION</span></strong><span style="color:black;background:#FFFF99">: This email originated from outside of the organization. Do not click links or open attachments unless
you can confirm the sender and know the content is safe.</span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">Hi, <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">I am trying to evaluate osd-zfs based MDS and OST deployment on a 2 node setup.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">I have the following questions about Lustre log:<o:p></o:p></p>
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<![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><b>Is changelog and llog both the same, in the sense are they synonymous with each other?</b><o:p></o:p></p>
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<![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>I understand that ZIL is currently not supported in Lustre version 2.12.2. My question is :
<o:p></o:p></p>
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<![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>My understanding is that transactions (in general) need some logging mechanism for it to work in 'all or none' scenarios. Please correct me if my understanding is incorrect. I understand that changelog has to be enabled so that filesystem
changes are recorded to be replayed after a crash. <b>How does Lustre transactions work if there is no intent log/changelog ?</b><o:p></o:p></p>
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<![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Does it mean that if changelog is NOT enabled and there is a crash, we risk losing all changes/updates to the filesystem ?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">Appreciate your timely response and Thank you for your help.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">-- <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:35.4pt">Regards<br>
<br>
Sudheendra Sampath<o:p></o:p></p>
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