https://jira.whamcloud.com This file is an XML representation of an issue en-us 9.4.14 940014 05-12-2023 https://jira.whamcloud.com/browse/LU-1707 Lustre <p>It would be valuable to programmatically discover the number of OSTs that are available. An <tt>llapi_*</tt> function would be a suitable place for this call.</p> <h3><a name="UseCase"></a>Use Case</h3> <p>When writing HDF5 files one typically configures the number of writers as a fraction of the number of OSTs for best performance. </p> <p>Currently this information is only available by writing a file with stripe count set to -1 and then counting the number of stripes present. A programmatic interface to the OST count would simplify this task.</p> LU-1707

Add llapi_* function to return the OST/MDT count for a path.

Improvement Minor Open Unresolved WC Triage Richard Henwood llnl Fri, 3 Aug 2012 10:58:49 +0000 Tue, 14 Jul 2020 06:43:00 +0000 0 7 <p>The current method is:</p> <ol> <li>Set a directory to stripe over the all OSTs <tt>lfs setstripe -c -1 ./</tt></li> <li>Write a file into the directory.</li> <li>Read the number of stripes the file has <tt>lfs getstripe -q</tt>. Count using string parsing.</li> <li>Delete the file, and the directory.</li> </ol> <p>The number of OST's on the system is available using the command:</p> <div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent"> <pre># lfs osts /mnt/lustre/ OBDS:: 0: lustre-OST0000_UUID ACTIVE 1: lustre-OST0001_UUID ACTIVE </pre> </div></div> <p>It seems like the function in <tt>lustreapi.h</tt> is </p> <div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent"> <pre>int llapi_ostlist(char *path, struct find_param *param); </pre> </div></div> <p>The documentation is, sparse. I'll try and rustle up a usage example.</p> <p>Just noticed this ticket/thread. I also need this functionality from within my code<br/> and Ned has recommended the undocumented function "llapi_get_obd_count" to get the <br/> required info in another thread. The problem/difficulty with it is apparently that it<br/> requires ioctl functionality to work, which is problematic on machines like sequoia.<br/> The current status right now is that it has a work around to avoid the ioctl, but <br/> I don't know how generally effective that workaround is. </p> <p>In any case, I'm glad it is more than just me that needs this...things are always<br/> more likely to get fixed when multiple wheels are squeaking <img class="emoticon" src="https://jira.whamcloud.com/images/icons/emoticons/smile.png" height="16" width="16" align="absmiddle" alt="" border="0"/></p> <p>Andy</p> <p>Do we really want to know how many OSTs are available or rather do we want to know what is the maximum stripe count we can get on a file? I suspect it is the latter. If so we should add a function whose name reflects this (say llapi_get_max_stripe_count(int fd/const char *path/...).</p> <p>Second, in the lustre source not all OBDs are OSTs, so if we want the OST count then the function should be llapi_get_ost_count().</p> <p>The thing I want is the maximum number of components I can stripe over from the point of view of my running application.<br/> I need that quantity for what appears to be exactly the same use case as Richard describes above...setting how many<br/> (and which) writers I should have.</p> <p>So something along the lines of your first suggestion seems the most appropriate for me.</p> <p>I'm not really clear on the differences, subtle and not so subtle, between the alphabet soup<br/> of ost's, obd's, oss's, mds's mdt's and so on, so I'll leave the second issue to you <img class="emoticon" src="https://jira.whamcloud.com/images/icons/emoticons/smile.png" height="16" width="16" align="absmiddle" alt="" border="0"/></p> <p>Andy </p> <p>John: thanks for your thoughts on this.</p> <p>Can you provide an example when: the # of available OSTs != maximum stripe count?</p> <p>IIRC any system with more than 2000 OSTs will have this property.</p> <p>I understand. My interpretation is now that both Andy and myself do want the 'maximum stripe count', as you suggested.</p> <p>An even simpler case: A filesystem has 100 OSTs, but one is marked inactive. The function should return 99 in that case.</p> <p>While looking at <a href="https://jira.whamcloud.com/browse/LU-2182" title="Add llapi_file_get_layout() function in liblustreapi" class="issue-link" data-issue-key="LU-2182"><del>LU-2182</del></a> I noticed this ticket. This functionality has been implemented as </p> <p>int llapi_get_obd_count(char *mnt, int *count, int is_mdt)</p> <p>If this fits what you are looking for then let us know so this ticket can be closed.</p> <p><br/> See my above comment of 4:42 Dec 6, 2013, re llapi_get_obd_count in the context of closing this ticket.</p> <p>Yep, I also just had this discussion with Ned.a few minutes ago. This overlaps the work I'm doing in <a href="https://jira.whamcloud.com/browse/LU-5030" title="&quot;lctl {get,set}_param&quot; should also check in /sys/fs/{lnet,lustre}" class="issue-link" data-issue-key="LU-5030"><del>LU-5030</del></a> so I will get around to implementing this for you. Looks like I will have to focus my time toward <a href="https://jira.whamcloud.com/browse/LU-5030" title="&quot;lctl {get,set}_param&quot; should also check in /sys/fs/{lnet,lustre}" class="issue-link" data-issue-key="LU-5030"><del>LU-5030</del></a> first.</p> <p>Ned, does the new llapi_layout_* functionality landed via <a href="http://review.whamcloud.com/5302" class="external-link" target="_blank" rel="nofollow noopener">http://review.whamcloud.com/5302</a> or is there still work to be done?</p> <p>The functionality described in the description of this issue is still lacking in the API. A set of new interfaces is needed that implements John's suggestion from <a href="https://jira.hpdd.intel.com/browse/LU-3840?focusedCommentId=89285&amp;page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-89285" class="external-link" target="_blank" rel="nofollow noopener">this</a> comment.</p> <p>Adding this as a requirement to <a href="https://jira.whamcloud.com/browse/LU-5969" title="Create an LGPL version of liblustreapi" class="issue-link" data-issue-key="LU-5969">LU-5969</a>. </p> Related LU-2182 LU-5969 Development Rank 1|hzw2nz: Rank (Obsolete) 10514