What Happens With VMFS3 LUNs Greater Then 2 TB
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.