One of the new features of vSphere is the ability to grow a volume/extent. This way you don’t have to add additional extends/lun’s to grow a datastore.
However trying to a grow a volume with vCenter on a ESXi 4 host didn’t work for me. If I clicked on the "Increase" button, a pop-up for Increase DataStore Capacity came up, but it was blank.
vCenter reports 110 GB on the device and 100 GB capacity on the extent. So vCenter did recognize the increase of the lun, but I wasn’t able to use the ability to grow an extent.
After some research I found out that the ability to grow a volume/extent does work on new created datastores on vSphere.
However under some circumstances a datastore upgraded from ESX 3.5 cannot be not be grown from the vSphere client through vCenter. But when you connect directly to the ESX host it can be upgraded! vCenter now presents the datastore as expandable.
Not possible when done via vCenter. How strange?
vKnowledge 
I had this exact issue today and your post solved it for me.
I agree…very strange…why does the host allow it but not through vCenter?
The only difference I could see is that VMFS Volumes created in 3.5 are VMFS 3.31, and in 4.0 they are version 3.33. Perhaps this has something to do with it?
My guess it has something to do with vCenter which can not remotely extend a VMFS 3.31 volume. Perhaps it will be fixed in the next vCenter update.
Cheers,
I experienced this issue today with vCenter 4.1.0 and ESXi 4.1 . I was able to solve it the same way.. thanks a lot!
heckmeck
Gracia amigo, he tenido el mismo problema el día de hoy y lo he resuelto con su ayuda. excelente post, muchas gracias.
thanks, you solved my problem 🙂
greetings from Poland