We're thinking about getting the vmware suite (VMware vSphere 4.1 Essentials Plus Kit). What I would like to know, if the vCenter Server is critical for High Availability feature.

1) Is cluster functional even if vCenter Server crashes? Are the VM protected in that case, or it fails completely?
2) Does the vCenter server have to be on same LAN ?


1) Your VM's will all continue to work if vCenter crashes, however you will lose the most of the functionality vCenter provides - so no live migrations, however HA will still work. This is because vCenter is required to configure HA, but it sets it up so that it is not required for it to function. In practice we've found that removing vCenter primarily only impacts your ability to make changes, but things run smoothly without it.

2) It does not have to be on the same VLAN, it can be anywhere on your network that can communicate with the ESX(i) hosts.

As an aside when we first setup our cluster we were told running vCenter on a VM inside of the cluster it was managing worked fine - we were skeptical but tried it. It's worked fantastic for the last nearly 4 years with no problems. It seems deeply wrong somehow - but it works great.

(Edited answer to #2 to reflect correction in comments)

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    No, vCenter can be anywhere on your network that both the vCenter server and the ESX(i) hosts can communicate with. – SpacemanSpiff Jun 2 '11 at 13:26
  • Ok, great! So does anybody think that running vCenter in VM is a bad idea? Otherwise I will do it as well. Another thing, a bit offtopic, in description of vmware essential kit I found this (VMware vSphere Essentials Plus includes: * VMware ESXi or VMware ESX hypervisor architecture (deployment-time choice, VMware recommends the ESXi hypervisor architecture) . Why do they prefer ESXi over ESX ? – John Jun 2 '11 at 13:30
  • It can be a problem if the physical box that runs the vCenter vm goes down. You can connect the vmware client directly to another esx box and register the vCenter vm, but then when you get the other box back up, it is registered in two places. However Vmware does handle this gracefully. This has only been an issue once in 5 years, and it wasn't that big a deal. The benefits, I would say, outweigh the risks. – James Jun 2 '11 at 14:01
  • @SpacemanSpiff thanks for correcting me on that. @Mejmo VMware has stated that 4.1 is the last release they will do for ESX, and all future releases will be ESXi, so I would just start out with ESXi and save yourself the hassle of transitioning later. – Neil Neely Jun 2 '11 at 14:50
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    ESX let's you do things that VMware would rather you didn't - like install your own code to run on the hypervisor. If you aren't aiming for doing really custom things to your hypervisor then this likely won't matter to you. VMware breaks it down in more detail here vmware.com/products/vsphere/esxi-and-esx/faqs.html – Neil Neely Jun 2 '11 at 15:19
  1. The cluster is functional while vcenter is down. DRS is unavailabale but HA is still operational.
  2. No, but is there some reason why you couldn't put the management nics on the same lan as vcenter?

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