This is in no way hot news but I wanted to write it down anyway.
I am currently working on upgrading some VMware ESX 2.5 servers to ESX 3.0.2. We have opted for a rolling upgrade by installing one of the servers with 3.0.2, adding a new LUN, format it with VMFS3 and then migrating servers of the old servers and LUNs and then reinstalling the server. The new VMFS was formated with standard options (but not by me).
Then, when moving one of the last servers of the machine I wanted to reinstall I got this:
A general system error occurred: File [OldLUN]:MySuperserver.vmdk is larger than the maximums size supported by datastore NewLun.
Oh, the horror.
It turns out that the maximum file sizes supported by a given block size has changed.
Max file size Block size 256 GB 1 MB 512 GB 2 MB 1024 GB 4 MB 2048 GB 8 MB
It seems there is no way around this other than vacating the datastore and trying again.