NetApp LUN Expansion Limit

Yesterday we were working on expanding a drive for one of our SQL servers in VMWare.  Ordinarily we have all our guest drives as .vmdk files, but this SQL server is clustered so it is a Raw Device Mapping (RDM) to a LUN on the NetApp.  We have expanded LUNs like this in the past and not had any issues.  This time we did have issues and it took a bit of searching to figure it out.

This server is not yet in production so some of the volumes were not sized how they were going to be when it goes live.  In this case we were upping a volume to the size it needed to be to go into prod.  This meant going from 40gb up to 500gb to support all the data that would be imported.  At this point we got an error on the NetApp  “New size exceeds this LUN’s initial Geometry.”  After a bit of Googling we found a forum post that NetApp has a limit to the amt you can expand a LUN restricting it to no more than 10x the original size.  I imagine that for most folks this would not be a problem, but if you are like us and going from test/validation to prod on the same LUN and need to expand you could paint yourself into a corner as we did.

We had to blow-away the LUN and recreate it, which ended up being a major pain due to the clustered servers.  The lesson is, size your volumes to an appropriate size initially, or be prepared to do some file copying later on if you reach the limit.

2 thoughts on “NetApp LUN Expansion Limit”

  1. Thanks for the comment!
    Unfortunately that was not the experience that we had. We tried going up in increments and ultimately never got there. We went from 40g to 200g which worked, then to 300g, then to 400g, and when we tried going from 400g to 450g it failed. We then inched it up little by little by 5s until we got to 445g where it failed again. The highest we were ever able to get it was 443g (which isn’t exactly 10x but go figure).

    I’d be interested to hear others experiences.

  2. Even though you’ve already blown away the original LUN and this is sort of a moot point – the 10x original size restriction applies only for each time that you grow the LUN. So you could have grown the LUN from 40GB to 400GB the first time around and then grown it again from 400GB to 500GB to finish it off.

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