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VMFS/LUN size?

by Roger Lund

I get this question often, in fact I had this question at our first local user group.

My Answer was 500 GB, or very close to it,  here is a post by http://www.yellow-bricks.com titled : VMFS/LUN size?


“A question that pops up on the VMTN Community once every day is what size VMFS datastore should I create? The answer always varies,  one says “500Gb” the other says “1TB”. Now the real answer should be, it depends.

Most companies can use a simple formula in my opinion. First you should answer these questions:

  • What’s the maximum amount of VMs you’ve set for a VMFS volume?
  • What’s the average size of a VM in your environment? (First remove the really large VM’s that typically get an RDM.)

If you don’t know what the maximum amount of VMs should be just use a safe number, anywhere between 10 and 15. Here’s the formula I always use:

round((maxVMs * avgSize) + 20% )

I usually use increments of 25GB. This is where the round comes in to play. If you end up with 380GB round it up to 400GB and if you end up with 321GB round it up to 325GB. Let’s assume your average VM size is 30GB and your max amount of VMs per VMFS volume is 10:

(10*30) + 60 =360
360 rounded up –> 375GB”

Source Post http://www.yellow-bricks.com/2009/06/23/vmfslun-size/

Seems to me a good method of scaling your datastore sizes.


I also saw this NetApp Article, referring to the above post.

What’s the right LUN size for a VMFS datastore?

I can’t tell you how often we are asked this question and the answer has many variables including the amount of aggregated I/O of the servers being virtualized onto the datastore, the storage protocol used in connecting to the datastore, etc.

I believe Duncan Epping at Yellow Bricks has provided us with a simple answer to this traditionally difficult question. Hopefully you’re very familiar with Duncan, he’s an active contributor to the VMTN and his site is one of the top VMware blog sites that is always brimming with the type of information that can significantly improve your VMware deployment.
I compliment Duncan on the way he phrased his guidance. I believe we may want to consider rewording the recommendations currently in TR-3428 (VI3) and the upcoming TR-3749 (vSphere). BTW – the current guidance in both of these documents is a LUN ranging in size from 300 GB – 700 GB.
Go check out Duncan’s post, it contains very solid guidance to this long running question, and may I suggest you drop him a note for his thoughts on sizing a NFS datastore. “

Source Post http://blogs.netapp.com/virtualstorageguy/2009/06/whats-the-right-lun-size-for-a-vmfs-datastore.html

Both Good Reads, enjoy.

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