With the installation of VMware ESXi 4, data stores will automatically be created using the default settings. This includes a block size of 1 MB. If you don't want that, you could delete the empty datastore and create a new one.
Sometimes, deleting the empty datastore fails with the message:
VMware's KB 1017104 provides the solution for another problem, but this works just as well with this issue, with a little variation.
The steps to resolve are:
esxcfg-scsidevs –l | grep –I naa
The partition table has been altered!
After it's gone, you can recreate a new datastore. Note that traces of the partitions will still be present. When creating the store, select to use all free space. This will get rid of the remnants of the previous partitions.