we have the following situation: ESX 3.5 without local hard disk, ESX boots from SAN. The LUN is about 20 GB and partitioned like this:
8 GB /
100 MB /boot
500 MB /home
1 GB /tmp
8 GB /var
There is no local VMFS, because with ESX 3.5 and boot from SAN there was no reason to have one. Now with ESX 4 I have to move the SC to the esxconsole.vmdk on a local (or private) VMFS volume. How would I do that? Is there any way to avoid reinstalling ESX 4 from scratch to the existing LUN or creating a 2nd SAN LUN and mask it to the ESX privately?
You can go with the default Host Upgrade Using the Upgrade utilities, vCentre Update Manager (VUM) or vSphere Host Update Utility (vHUU). It will do the inplace host upgrade from 3.5 to 4.0.
vHUU is a freeware, you can install it along with the vSphere Client 4.0. Once you install vHUU add the 3.5 host to it for upgrade.
Start upgrade procedure with the "Upgrade wizard" in vHUU. The steps are clear and streight forward. In between , the wizard will ask for you to choose the VMFS datastore for COS vmdk.
In your case, choose the VMFS data store whic's in SAN.
Before vHUU starts the upgrade, it will do a host compatibility check to make sure that the host is compatible for upgrade.
The detailed steps for 3.5 to ESX4.0 upgrade are available in vSphere 4.0 Upgrade guide.
If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful.