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<p class="MsoNormal">Hi all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We are reviewing some of our configurations and were not sure what to make of the NSD Device Types that GPFS uses and what, if anything, do they change about how GPFS accesses/recovers/manages/etc the underlying storage based on this setting.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The documentation doesn’t say much about it other than to consult the /usr/lpp/mmfs/bin/mmdevdiscover command (no man page), which has this section:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># Known disk types currently are:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">#<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># powerdisk - EMC power path disk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># vpath - IBM virtual path disk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># dmm - Device-Mapper Multipath (DMM)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># dlmfdrv - Hitachi dlm<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># hdisk - AIX hard disk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># lv - AIX logical volume. Historical usage only.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># Not allowed as a new device to mmcrnsd.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># gpt - GPFS partition on Windows disk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># generic - Device having no unique failover or multipathing<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># characteristic (predominantly Linux devices).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""># dasd - DASD device (for Linux on z Systems)<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We have our storage under Linux Device-Mapper Multipath control (two device paths to all storage, active/passive) and are accessible under /dev/mapper, but the NSD types are current set to ‘generic’ not ‘dmm’. This is configured in the
/var/mmfs/etc/nsddevices file:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">if [[ $osName = Linux ]]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">then<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> : # Add function to discover disks in the Linux environment.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> ls -l /dev/mpath/ 2>/dev/null | awk '{print "mpath/"$9 " generic"}'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> ls -l /dev/mapper/ 2>/dev/null | awk '{print "mapper/"$9 "
<span style="background:yellow;mso-highlight:yellow">generic</span>"}'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> ls -1 /dev/vd* 2>/dev/null | awk -F '/' '{print ""$3 " generic"}'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">fi<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Can somebody from IBM explain what the correct setting should be and what differences GPFS does with ‘generic’ vs. ‘dmm’ vs. others?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance!<o:p></o:p></p>
<p class="MsoNormal">-Bryan<o:p></o:p></p>
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