What Happens With VMFS3 LUNs Greater Then 2 TB
September 19, 2011 
Sean Crookston 
I had someone run into an issue earlier in the day that I couldn’t’ explain in regards to a datastore size. We found the LUN size itself was greater then 2 TB, which was acknowledged as not being supported but the amount of space that did become available did not make sense.
So we all know that there is a 2 TB-512 LUN size limit for VMFS3, but do you know what size LUN you will be presented with when you present a LUN bigger than this?
Lets say we add a new VMFS3 volume on a presented LUN that is 3,5 or 7 TB? One would expect that you would then receive a 2TB LUN at least, but in actuality you will end up with a 1 TB LUN. How about a 3.5,5.5, or 7.5 TB volume? You would end up with a 1.5 TB LUN in each of these cases.
I looked for a knowledgebase to back this but could only find one community posting which alluded to the LUN size being based on the remainder of what was presented after taking 2 TB chunks out at a time. This means you could end up with some really weird sizes you weren’t expecting.
*Note-Frank Denneman(http://frankdenneman.nl) made an important observation that this information only applies to VMFS3. This entry has been updated to reflect that this information applies to VMFS version 3. VMFS version 5 will support a 64TB LUN.
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The 64TB LUN size only applies to RDMs. VMFS5 is still limited to 2TB
Would you be able to provide any information or documentation on that limitation? From my reading of the vSphere 5 Config Maximum guide and posts such as the below the limitation is 64 TB for a single extent datastore.
The limitation for a single VMDK however remains at 2TB-512 and a physical RDM would be necessary to go beyond that.
http://blogs.vmware.com/vsphere/2011/08/how-big-can-i-make-a-single-extent-vmfs-5-datastore.html
Hey Sean,
See VMware KB Article: 2003813.
I was mistaken in that what I saw as a standard VMFS-5 datastore was in fact referring to the non-passthrough RDM, which is still limited to 2TB.
It seems that the VMFS-5 datastore does as you stated, support up to 64TB.
My Apologies…