with vsphere, RDMs can be converted into vmdk files by using the datastore migration feature. however, to accomplish this you must choose a thick or thin conversion. using the “same as source” option will only transfer the RDM pointer files and not accomplish much. hot/live migrations have worked out just fine several times. also if cold datastore migrations are failing repeatedly try a hot migration (oddly enough it seems to have a higher success rate).

also on vmfs volumes…in our instance we seemed limited to 1.99TB volumes and could not create 2TB or greater volumes for some reason, despite max vmfs volume size being 64TB.

update 11/7/2011:
you can use extents to create datastores greater than 1.99TB, i’ve only dabbled with it however. just today i learned that VMFS5 (ships with vsphere 5) will support up to 64TB on a single extent.

update 5/29/2013:
my last update is absolutely true despite bickering and misinformation in various internet forums. in vsphere 4.x you simply cannot create a single extent VMFS datastore over 2TB.
source: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2007328

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