Huckfinn,
No, I haven't figured it out yet, I am attempting to locate some spare equipment so I can set up a test environment to test the procedure. What I am afraid of is that the newly installed host will see the lun but not mount it as it is, but will want to format it instead. I need to preserve the existing virtual machines intact on the existing lun, and attach it to the new host. Skimming other forums on similar topics it seems that as long as the new host has been added to a cluster, then the iscsi luns will be marked as "sharable" so there will be no issues, but then I read in other posts that this should be possible without formatting the existing lun with either paid product cluster hosts or standalone free hypervisor hosts. And in still other postings I read that the only way to attach the existing lun to the new host is to reformat it and start over, so it looks like the only way to find the answer to my question is to set up a test environment and try it before I wipe the production 4.1 esx hosts and install esxi 5.1.
Regarding your question about vmfs datastore options for the local datastore (i.e. hard drives installed in the server, not the iscsi luns) if any virtual machines or other data have been moved off of it, I would overwrite the vmfs datastore. If I understand correctly, it is now possible to do an in place upgrade from classic ("fat") esx to esxi, which I believe the "Migrate ESX, preserve vmfs datastore" would do, so it would not be a clean install. Preserving the existing local vmfs datastore would also not be a clean install, so I am planning to overwrite the local vmfs datastore (I will be detaching the iscsi network cables prior to starting the install just as you are, so there won't be any confusion about which disk to install on). As I am building a new virtual center I will be removing the host from the old cluster and adding it to the new cluster in the new virtual center after the installation.
If anyone in this forum has previously done a wipe and reinstall of their hosts attached to an iscsi san, could you please post what you did to attach the existing iscsi luns to the newly re-installed hosts intact, preserving the production virtual machines on the volume?