Expand LUNs with ESX and not vCenter

April 2, 2011 · 1 comment

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When we upgraded to vSphere 4.1, there was nothing different about the way we expanded LUNs.  We have three EqualLogic iSCSI SAN arrays for storage and two IBM BladeCenters.  If we needed more space, the process was quite simple

  • go to the web interface of the SAN and expanded the LUN
  • using vCenter, click on a host that was using the LUN (we have the servers in an HA/DRS cluster), go to Configuration->Storage and click on the LUN you just expanded.
  • in the Datastore Details, click on Properties and when the Volume Properties dialog box comes up, click on the “Increase…” button
  • in the Extent Device dialog box, you c an select the LUN and complete the process

However, we recently added a Compellent SAN array, and started moving a number of LUNs over to it.  Everything was going great until we attempted to increase the size of a LUN.  When we go the the Extent Device dialog box there was nothing displayed.  When we  back to the Storage Adapters section on the Configuration  page in vCenter, it correctly showed the new increased capacity of the LUN so it did not appear that Compellent was doing anything wrong.  We tried a number of tests, but in every case we could not increase the VMFS space on an expanded LUN.

Since we have support from VMware, we decided to open a support case with them.  During a web-sharing session with the engineer, we looked at every configuration and option within vCenter and the ESX hosts.  We tried bouncing a host (after moving to maintenance mode and migrating all the clients with DRS) and still nothing.  After three hours, we were out of ideas and things to try.

When it seemed impossible to move forward, the support engineer called out to a developer to see if he could give us some help.  After about two minutes of listening to our predicament, he simply said, “You can’t do that with vCenter.  Just go on to the ESX host web interface and do it from there.  The vCenter is not always consistent with ESX and the LUNs, so you have to use the host interface if you want it to work correctly.”

Surprised, we brought up the ESX web interface and proceeded to expand the LUN without a problem.  I told the developer that VMware documentation specifically stated to use vCenter for this purpose as did some other articles.  The support engineer agreed.  The developer simply chuckled and said he knew what worked and how it worked.  And he was right.

So, if you want to be able to consistently increase your storage space on your SAN for vSphere, do it from the ESX host and you are off and running.

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Article by Steve Van Domelen

Steve has written 47 awesome articles.

  • Ozorknai

    Thanks for the info, I had exactly the same issue. I could not extend the LUN from VC, but I was able to do it from the ESX host with no problem. You saved me opening a service call to VMware.  

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