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Hi All,
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<div class="">My thanks to Aaron, Sven, Steve, and whoever responded for the GPFS team. You confirmed what I suspected … my example 10 second I/O was _from an NSD server_ … and since we’re in a 8 Gb FC SAN environment, it therefore means - correct me if I’m
wrong about this someone - that I’ve got a problem somewhere in one (or more) of the following 3 components:</div>
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<div class="">1) the NSD servers</div>
<div class="">2) the SAN fabric</div>
<div class="">3) the storage arrays</div>
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<div class="">I’ve been looking at all of the above and none of them are showing any obvious problems. I’ve actually got a techie from the storage array vendor stopping by on Thursday, so I’ll see if he can spot anything there. Our FC switches are QLogic’s,
so I’m kinda screwed there in terms of getting any help. But I don’t see any errors in the switch logs and “show perf” on the switches is showing I/O rates of 50-100 MB/sec on the in use ports, so I don’t _think_ that’s the issue.</div>
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<div class="">And this is the GPFS mailing list, after all … so let’s talk about the NSD servers. Neither memory (64 GB) nor CPU (2 x quad-core Intel Xeon E5620’s) appear to be an issue. But I have been looking at the output of “mmfsadm saferdump nsd” based
on what Aaron and then Steve said. Here’s some fairly typical output from one of the SMALL queues (I’ve checked several of my 8 NSD servers and they’re all showing similar output):</div>
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<div class=""> Queue NSD type NsdQueueTraditional [244]: SMALL, threads started 12, active 3, highest 12, deferred 0, chgSize 0, draining 0, is_chg 0</div>
<div class=""> requests pending 0, highest pending 73, total processed 4859732</div>
<div class=""> mutex 0x7F3E449B8F10, reqCond 0x7F3E449B8F58, thCond 0x7F3E449B8F98, queue 0x7F3E449B8EF0, nFreeNsdRequests 29</div>
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<div class="">And for a LARGE queue:</div>
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</span></div>
<div class=""> Queue NSD type NsdQueueTraditional [8]: LARGE, threads started 12, active 1, highest 12, deferred 0, chgSize 0, draining 0, is_chg 0</div>
<div class=""> requests pending 0, highest pending 71, total processed 2332966</div>
<div class=""> mutex 0x7F3E441F3890, reqCond 0x7F3E441F38D8, thCond 0x7F3E441F3918, queue 0x7F3E441F3870, nFreeNsdRequests 31</div>
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<div class="">So my large queues seem to be slightly less utilized than my small queues overall … i.e. I see more inactive large queues and they generally have a smaller “highest pending” value.</div>
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<div class="">Question: are those non-zero “highest pending” values something to be concerned about?</div>
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<div class="">I have the following thread-related parameters set:</div>
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<div class="">[common]</div>
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<div class="">maxReceiverThreads 12</div>
<div class="">nsdMaxWorkerThreads 640</div>
<div class="">nsdThreadsPerQueue 4</div>
<div class="">nsdSmallThreadRatio 3</div>
<div class="">workerThreads 128</div>
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<div class="">[serverLicense]</div>
<div class="">nsdMaxWorkerThreads 1024</div>
<div class="">nsdThreadsPerQueue 12</div>
<div class="">nsdSmallThreadRatio 1</div>
<div class="">pitWorkerThreadsPerNode 3</div>
<div class="">workerThreads 1024</div>
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<div class="">Also, at the top of the “mmfsadm saferdump nsd” output I see:</div>
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<div class="">Total server worker threads: running 1008, desired 147, forNSD 147, forGNR 0, nsdBigBufferSize 16777216</div>
<div class="">nsdMultiQueue: 256, nsdMultiQueueType: 1, nsdMinWorkerThreads: 16, nsdMaxWorkerThreads: 1024</div>
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<div class="">Question: is the fact that 1008 is pretty close to 1024 a concern?</div>
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<div class="">Anything jump out at anybody? I don’t mind sharing full output, but it is rather lengthy. Is this worthy of a PMR?</div>
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<div class="">Thanks!</div>
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<div style="color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
<div class="">Kevin Buterbaugh - Senior System Administrator</div>
<div class="">Vanderbilt University - Advanced Computing Center for Research and Education</div>
<div class=""><a href="mailto:Kevin.Buterbaugh@vanderbilt.edu" class="">Kevin.Buterbaugh@vanderbilt.edu</a> - (615)875-9633</div>
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<div class="">On Feb 17, 2019, at 1:01 PM, IBM Spectrum Scale <<a href="mailto:scale@us.ibm.com" class="">scale@us.ibm.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class=""><span style=" font-size:10pt;font-family:sans-serif" class="">Hi Kevin,</span><br class="">
<br class="">
<span style=" font-size:10pt;font-family:sans-serif" class="">The I/O hist shown by the command mmdiag --iohist actually depends on the node on which you are running this command from.</span><br class="">
<span style=" font-size:10pt;font-family:sans-serif" class="">If you are running this on a NSD server node then it will show the time taken to complete/serve the read or write I/O operation sent from the client node.
</span><br class="">
<span style=" font-size:10pt;font-family:sans-serif" class="">And if you are running this on a client (or non NSD server) node then it will show the complete time taken by the read or write I/O operation requested by the client node to complete.</span><br class="">
<span style=" font-size:10pt;font-family:sans-serif" class="">So in a nut shell for the NSD server case it is just the latency of the I/O done on disk by the server whereas for the NSD client case it also the latency of send and receive of I/O request to the
NSD server along with the latency of I/O done on disk by the NSD server.</span><br class="">
<span style=" font-size:10pt;font-family:sans-serif" class="">I hope this answers your query.</span><br class="">
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<span style=" font-size:10pt;font-family:sans-serif" class="">Regards, The Spectrum Scale (GPFS) team<br class="">
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<span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif" class="">From: </span><span style=" font-size:9pt;font-family:sans-serif" class="">"Buterbaugh, Kevin L" <<a href="mailto:Kevin.Buterbaugh@Vanderbilt.Edu" class="">Kevin.Buterbaugh@Vanderbilt.Edu</a>></span><br class="">
<span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif" class="">To: </span><span style=" font-size:9pt;font-family:sans-serif" class="">gpfsug main discussion list <<a href="mailto:gpfsug-discuss@spectrumscale.org" class="">gpfsug-discuss@spectrumscale.org</a>></span><br class="">
<span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif" class="">Date: </span><span style=" font-size:9pt;font-family:sans-serif" class="">02/16/2019 08:18 PM</span><br class="">
<span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif" class="">Subject: </span><span style=" font-size:9pt;font-family:sans-serif" class="">[gpfsug-discuss] Clarification of mmdiag --iohist output</span><br class="">
<span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif" class="">Sent by: </span><span style=" font-size:9pt;font-family:sans-serif" class=""><a href="mailto:gpfsug-discuss-bounces@spectrumscale.org" class="">gpfsug-discuss-bounces@spectrumscale.org</a></span><br class="">
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<span style=" font-size:12pt" class="">Hi All, </span><br class="">
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<span style=" font-size:12pt" class="">Been reading man pages, docs, and Googling, and haven’t found a definitive answer to this question, so I knew exactly where to turn… ;-)</span><br class="">
<br class="">
<span style=" font-size:12pt" class="">I’m dealing with some slow I/O’s to certain storage arrays in our environments … like really, really slow I/O’s … here’s just one example from one of my NSD servers of a 10 second I/O:</span><br class="">
<br class="">
<span style=" font-size:12pt" class="">08:49:34.943186 W data 30:41615622144 2048 10115.192 srv dm-92 <client IP redacted></span><br class="">
<br class="">
<span style=" font-size:12pt" class="">So here’s my question … when mmdiag —iohist tells me that that I/O took slightly over 10 seconds, is that:</span><br class="">
<br class="">
<span style=" font-size:12pt" class="">1. The time from when the NSD server received the I/O request from the client until it shipped the data back onto the wire towards the client?</span><br class="">
<span style=" font-size:12pt" class="">2. The time from when the client issued the I/O request until it received the data back from the NSD server?</span><br class="">
<span style=" font-size:12pt" class="">3. Something else?</span><br class="">
<br class="">
<span style=" font-size:12pt" class="">I’m thinking it’s #1, but want to confirm. Which one it is has very obvious implications for our troubleshooting steps. Thanks in advance…</span><br class="">
<br class="">
<span style=" font-size:12pt" class="">Kevin</span><br class="">
<span style=" font-size:12pt" class="">—</span><br class="">
<span style=" font-size:12pt" class="">Kevin Buterbaugh - Senior System Administrator</span><br class="">
<span style=" font-size:12pt" class="">Vanderbilt University - Advanced Computing Center for Research and Education</span><br class="">
<a href="mailto:Kevin.Buterbaugh@vanderbilt.edu" class=""><span style=" font-size:12pt;color:blue" class=""><u class="">Kevin.Buterbaugh@vanderbilt.edu</u></span></a><span style=" font-size:12pt" class="">- (615)875-9633</span><br class="">
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