Introduction

There are at least 3 solutions to have HA for vCenter Server:

• use a VM for VC and use VMware HA
• use vCenter Server Heartbeat product
• use a MSCS solution for VC

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VMware HA

http://www.vmware.com/products/high-availability/

Only usable when vCenter Server is a VM!
VMware HA require vCenter Server only for the initial setup and configuration.
Than it can work on ESX in a distributed mode, and vCenter Server is not needed to ensure the correct work of HA.
For this reason VMware HA can handle also vCenter Server restart (in this case the downtime could be some minutes...)

IMHO, for small/medium environment I prefer the VMware HA solution... very simple and cheap.
Be sure to have also the vCenter DB on your VM, or you have to find a HA solution also for your DB.

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vCenter Server Heartbeat

http://www.vmware.com/products/vcenter-server-heartbeat/

In this case vCenter Server (the primary instance) could be a VM or a physical system. The secondary must be a VM!
Optimize availability and resiliency for VMware vCenter Server in any situation. VMware vCenter Server Heartbeat delivers the maximum uptime for your virtual datacenter infrastructure, ensuring consistent operation, even when VMware vCenter Server is threatened by unplanned or planned downtime.

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MSCS or Failover Cluster

http://www.vmware.com/pdf/VC_MSCS.pdf
http://viops.vmware.com/home/docs/DOC-1111 - Reference Implementation: Clustering VirtualCenter 2.5 Using Microsoft Cluster Services

In this case vCenter Server (both the primary and the secondary node) could be a VM or a physical system!
You also need at least Windows Server 2003 (or 2008) Enterprise Edition.
Note that vCenter Server 2.5 is not supported on Windows Server 2008!

Similar to this solution is the usage of other cluster solutions, for example Veritas Cluster:
http://searchservervirtualization.techtarget.com/news/article/0,289142,sid94_gci1341780,00.html

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Why not VMware FT?

Is it a good choice-using FT for virtual vCenter server redundancy?
Not yet... vCenter Server 4.0 require 2 vCPU (expecially if you have also a local DB).
FT 1.0 can work only with VM single vCPU.
For more information on FT see: VMware FT