Notes on the Throughput of Zerto Virtual Replication Appliances

This is an article about Zerto, the award-winning IT Resilience platform I was first exposed to in 2011 and loved so much that I joined the team in 2012. For help with any Zerto-specific terminology, see Zerto’s official product documentation.

Note: this post refers to Zerto Virtual Replication versions 6.x and earlier.

The Zerto VRA is running Debian and has a VMware Tools vmxnet3 adapter. This is a 10 Gbps vNIC. If we consider a single VRA with a single* 10 Gbps NIC, that gives us a 1.25 GB/s theoretical maximum throughput, at least before accounting for protocol overhead and a slew of additional factors.

What are those factors which impact throughput on a LAN or between data centers? Turns out it doesn’t matter whether we’re talking about Zerto or any other technology, everything is impacted by one or more of the factors below:

• Network devices: your routers, switches, gateways, load balancers, and then all of the ISP’s gear…
• Network services: your MPLS, VPN, QoS, bandwidth shaping, and then all of your ISP’s services configurations…
• Network overheads and limits: hypervisor offload, frame rate limits, packet-per-second limits, max-concurrent-connection limits, latency, end-to-end MTU configurations, other application workloads…
• Security devices: firewalls, any host security hardware such as data encryption modules or encrypted NICs
• Security services: Intrusion Detection, Intrusion Prevention, other network filtering services; any host security software such as host anti-virus
• Recovery Site storage: read/write split, RAID type, caching, backplane performance, compression, deduplication, latency, other application workloads again…

I’ve seen performance held up by storage factors far more frequently than other factors, primarily because many businesses put little investment in their Recovery Site data centers. As older storage arrays continue to be replaced by modern equipment, and as IT Resilience continues its rapid ascent on the list of CIO and CTO priorities, I believe we’ll see this change for the better.

* Additional virtual NICs will not improve throughput.