Stretched Cluster Installation (HX 4.0)

For the Cisco Live US 2019 HyperFlex Data Protection Deep Dive breakout, I needed a HyperFlex 4.0 Stretched cluster to show some failures that can be beaten. In this post I will show the steps to install a stretched cluster (or synchronous replication cluster)

What is a Stretched Cluster ?

If you want to have a system with zero recovery point objective (RPO) you can use synchronous replication. This mean that the data is written on one site and at the same time at another site. The acknowledge will take place after all blocks are written on both sites.

To make sure that both cluster can agree on eachother, you will need a witness server. This witness server should be on a 3rd site to be the most effective.

What is a Streched Cluster

Requirements :

For a stretched cluster you will need HyperFlex M5 servers. It doesn’t matters if they are 220 or 240. All Flash or not. As long as they are M5 servers.

On both sites, you will need a Fabric Interconnect pair with a Layer 2 network in between. The latency should be at max 5 ms RTT and 10 Gb or more.

You will also need a witness server. Just to make sure you got quorum. The HyperFlex witness server can be downloaded on and installed on a VMware environment.

Let’s start :

The installing of the witness server is simple. Make sure you got an ip address and install the .ova file you downloaded. You don’t have to do anything on the witness server. Just let it be.

witness server for Stretched Cluster

Start the HyperFlex Installer

Have the installer running on your laptop or on a VMware environment. Login and select : Create Cluster / Stretch Cluster

Stretched Cluster Installer start

First we have to configure the two sites. Let’s start with configuring SITE-A

Create UCS-M Site for Stretched Cluster

After filling in the credentials, you will see the servers that are unassociated. On those servers a HX Esxi image must be installed. The installer won’t do that for you. Have a look at this blog about cleaning your system before installing.

Select servers

The VLAN configuration should be the same on both sites, because between the two stretch clusters there is a Layer 2 network.

Configure VLANs
Lets start the configuration

When you have a UCS-Manager with already VLAN’s on it, it’s possible you will get the following warning. You can Skip Validations and the system will continue configuring.

UCS-M Validation Failed
HyperFlex installation successful

When one site is configured, don’t forget to do the same for the other site of the stretched cluster.

Now configure the other site of the Stretched Cluster

After the setup of the UCS Managers on both sites, we can start with creating the Cluster.

Create Stretch Cluster
Fill in credentials for the site.
Pick the right servers

Fill in the IP addresses of the system. You will see the difference between Management-Vlan and Data-Vlan.

IP addresses of the Stretched cluster servers.
Almost the last step

You can’t change the Replication Factor. For a stretched cluster it’s 2+2.

Configure the services and new passwords.
Configure Auto Support and Advanced networking

If you SSO is the vCenter server, you don’t have to put the long string into the text box. See the note when you hover over it.

Create a stretched cluster start.

Hooray ! Cluster is up and running.

HyperFlex is up and running

Post Install

In this post you can see how you perform a Post install after a HyperFlex installation. For the completeness here are some screenshots :

Go with SSH to the installer and perform post_install

Post_install on the installer.

This is a new cluster, so option 1 NEW/Existing Cluster has been choosen.

Fill in credentials
configure vmotion the easy way.
Run a health check.

Now that the cluster is up and running AND you did the post install, let’s create a Datastore. You CAN NOT create a datastore via the vCenter plugin. In this plugin you can’t pick a Site Affinity. So the datastore must created by the HyperFlex Connect.

Create data-store from HyperFlex Connect.

As you can see, you will have to pick a Site Affinity. In vCenter you can create some affinity rules if you like.

Datastore with affinity has been created.

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