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are esxi and my vm will down or not?becaase i'm worry about that, i hopefully when i'm upgrading a vCenter will not make a change for availability of my esx and vm for production
There is NO Downtime required for ESXi host or the VM's when upgrading the vCenter server. Go through the following KB's before starting the upgrade process if not done already
Overview of upgrading from vCenter Server 5.0 to vCenter Server 5.1
Upgrading to vCenter Server 5.1 best practices