VSM High Availability is optional but it is strongly recommended in a production environment.
High availability is accomplished by installing and configuring a secondary VSM.

For instructions on how to install and configure a Primary Cisco 1000v VSM on your vSphere environment please follow
configure-vsphere-and-cisco-nexus-1000v-connecting-to-nexus-5k-upstream-switches

Then come back to this post to learn how to install and configure a secondary VSM for high availability.

1) Check the redundancy status of your primary VSM

// Check Modules

// check HA status

2) Install the secondary VSM from the OVF.
Select to Manually Configure Nexus 1000v and just like the primary installation select the right VLANs for Control, Packet and Management.

When you get to this properties page:

Do not fill in any of the fields, just click next and Finish

3) Power on the Secondary VSM
The system setup script will prompt for the following:

Admin password // Choose your password
VSM Role: secondary // VSM will reboot
Domain ID: 100 // This must be the same domain ID you gave to the primary, I used 100

Once a VSM is set to secondary it will reboot.

4) Verify VSM high availability
Login to VSM and run:

VMware recommends that you run the Primary and the Secondary on different ESX hosts.

5) Test VSM switchover
From the VSM run system switchover to switch between the active and the standby VSMs.

That is it, now you have a highly available Cisco 1000v VSM infrastructure.