I created a VM with all the disks and configuration on one data store. That data store had been configured with the default 1 meg block size. I then configured another data store, but as I was configuring the vmfs I wanted larger block size. I used the 8 meg block size.
Before I added the second data store and added the disks to the Virtual Machine the Virtual Machine Snapshot worked good; but then I then noticed that I could no snapshot any more. The error I got was in part: "File is larger than the maximum size supported by data store".
The first obvious thing to me was, "shoot, I need to put all the vmdk(s) on the data store with the largest block size". To do this you have to do a Migrate of the data store. This is what is so cool about VMWARE with all the bells and whistles. If you have a drive (storage) filling up, you can just migrate the disks to another storage location while the machines are on. In my case, I shut it down because it was not in production anyway.
While doing a Migrate, I choose Data Store, and then Advanced on the next screen. Doing "Advanced" allowed me to pick and choose the different vmdk disks. I had 6 disks in this server and only wanted to move 4.
After it was done I powered on and tested the Snapshot. Still got same error. I did a little digging and it seemed like I had done the right thing, so I was perplexed. I asked a consultant and he said to open a case with VMWARE. I did. Surprisingly, I was on the right trail, but did not realize that I needed to move the "Configuration" file also. This puts all of the machine's files on the same Data Store. For this you do have to do a cold migrate.
I shut the VM down, and did the same steps I mentioned above, but this time while in the "Advanced" screen, I only chose the "Configuration File". Choose the same "data store" that the vmdk(s) were on and moved it. I did notice some extra messages I have not seen before. This referred to "registering with new host". That was interesting.
When it was done. I fired it up. I did a Snapshot. Voila! It worked.
One thing I noticed was that it took the VM out of the resource pool it was originally in. No biggie. I just dragged and dropped it back in.
VMWARE allowed me to do some heavy duty work without breaking much of a sweat. Pretty cool. I hope this helps somebody else.
For more information. Go to VMWARE's site and search on KB article 1012384