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.

Can Zerto Exclude Disks or Volumes From Replication?

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.

A customer asked the following:

I am trying to figure out if Zerto can completely ignore certain disks on a protected VM. We have database backup dump devices that we do not want to replicate. I realize there is a Temp Disk flag that can be set that will not replicate changes after Initial Sync but, from the documentation I have found, Zerto still appears to require an Initial Sync of that disk.

Zerto doesn’t have a feature to completely ignore a disk or volume in versions 6.x and earlier. Note that doesn’t mean the feature is present in later versions, it strictly means I’m limiting myself to the context of versions 6.x and earlier!

This doesn’t mean the task is impossible. It does mean you must start with an empty source volume when protecting the virtual machine (VM) in Zerto. Sounds easy enough though, right? As some applications don’t appreciate having their temp data files destroyed, you should verify with the application owner and/or vendor before trying the workaround below. This process also assumes you are starting with a VM that is not protected by Zerto:

  1. In the VM’s guest operating system (OS), follow the OS or application vendor’s process to empty the relevant volume of all data you wish to bypass from Initial Sync. This sometimes involves stopping any application from writing to the relevant volume and then deleting the files on the volume.
  2. In the Zerto User Interface, Create or Edit a Zerto Virtual Protection Group (VPG).
  3. Apply the configuration settings you intend to apply to the VPG but, at the Storage step of the Create/Edit VPG wizard, check the box labeled Temp Data for any/all relevant volumes:

    Create VPG wizard with Temp Data highlighted
    A VPG Wizard with the Temp Data feature highlighted
  4. Optionally, check the box labeled Thin if you wish to set the Recovery Volume to Thin Provisioned.
  5. Continue to apply any configuration settings you intend to apply to the VPG, and then click Done.

If you created a new VPG, the VPG will next undergo an Initial Sync. If you edited an existing VPG, the VPG will instead undergo a Volume Initial Sync. Regardless of Sync type, while the relevant volume won’t be ignored completely, you may notice the Sync time is shorter as it has been reduced by whatever time it would have taken to sync that volume back when all the data was present. Note I say, “may” because it’s possible Zerto will read the entire source disk, as is the case when the source disk is thick-provisioned.

The result of all this? If you applied step 5, the result is no space wasted on temp/swap data that is generally useless in a recovery event.

 

Upgrading VMware Tools on a Zerto VRA (Virtual Replication Appliance)

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.

If VMware vCenter alerts you to VMware Tools being outdated on a Zerto Virtual Replication Appliance (VRA), what do you do?

Like many modern virtual appliances, the Zerto VRAs are unmanaged. In other words, they operate without a need for user management or intervention. Zerto VRAs are deployed with the version of VMware Tools that Zerto approves for that version of the VRA. The Zerto Virtual Manager (ZVM) software manages the VRAs and there is rarely a need to spend time or effort on them. All upgrades to the VRAs are done through the ZVM interface.

If you have an internal policy demanding specific VMware Tools levels and you’re unable to file an exception request for unmanaged devices, which is unusual as even major government and private-industry regulations such as HIPAA, PCI, SOX and others allow for exceptions provided they are appropriately documented, I suggest reaching out to the Zerto Support Team through the MyZerto portal.