Creating a redundant network for write replication

If you plan to use Write-Back policy with write replication, you need to select a network in vSphere for write replication.

Here are a few options to create a write replication network.

1. Create a new port group in your existing virtual switch that has two teamed 10gbps NIC ports preferably across two different host NICs. Preferably don’t use the iSCSI NICs. Use the vmotion or management NICs, since vmotion / management network will be less stressed. Ideally use a new VLAN to isolate the write replication traffic. Gateway is not needed.

2. You can also add a new 2-port 10g NIC in each host, create a separate vSwitch and run the write replication traffic on this network.

3. If your vmotion network is already 10g with Jumbo Frames, then you can simply use the vmotion network for write replication. Make sure you use the ‘default TCP/IP’ stack and not the ‘vmotion stack’ for VirtuCache write replication traffic .

In all the above three cases, configure Jumbo Frames on the vswitch, vmkernel adapter and physical switch. Preferably use LACP and LLDP protocols, which helps reduce latencies further. And preferably use one 10g port each from two host NICs, which are connected to one port each on two different stacked switches.

On a related note, if for some reason the write replication network fails, you will not lose any data. The VMs will move from Write-Back mode to Write-Through mode, and the operational state in the ‘Virtual Machines’ tab in the VirtuCache GUI for the affected VMs will reflect this.