Voici ce qui nous préconise Duncan pour partitionner ESX 4 (vSphere) :

A while back I published an article on partitioning your ESX host. This was based on 3.5, and of course with vSphere this has slightly changed. Let me start by quoting a section from the install and configure guide.

You cannot define the sizes of the /boot, vmkcore, and /vmfs partitions when you use the graphical or text installation modes. You can define these partition sizes when you do a scripted installation.

The ESX boot disk requires 1.25GB of free space and includes the /boot and vmkcore partitions. The /boot partition alone requires 1100MB.

The reason for this is the fact that the service console is a VMDK. This VMDK is stored on the local VMFS volume by default in the following location: esxconsole-<system-uuid>/esxconsole.vmdk. By the way, “/boot” has been increased as a “safety net” for future upgrades to ESX(i).

So for the manual installations there are three partitions less to worry about. I would advise to use the following sizes for the rest of the partitions, and I would also recommend to rename the local VMFS partition during installation. The default name is “Storage1″, my recommendation would be “<hostname>-localstorage”.

Primary:
/     - 5120MB
Swap  - 1600MB
Extended Partition:
/var  - 4096MB
/home - 2048MB
/opt  - 2048MB
/tmp  - 2048MB

With the disk sizes these days you should have more than enough space for a roughly 18GB for ESX in total.

http://www.yellow-bricks.com/2009/05/27/partitioning-your-esx-host-part-ii/