Re: VM grew to 258GB on datastore formatted with a 1M block size

Where are you getting the 258GB number from - the datastore browser?

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1012384

has info on VMFS overheads behind this and the workarounds you can use.

Upgrading to VMFS-5 won't help, because the 1MB block size would be retained as part of the upgrade.