Category Archives: BC/DR

Zerto – A game changer for DR

In our industry, Disaster Recovery or DR has always been a difficult discussion for a lot of people. It’s typically something that most organization don’t want to tackle for a variety of reasons. These reasons range from the complexity from a technology standpoint to the financial obligation that’s needed for an effective DR strategy. With the advent of virtualization made was a major step in make DR more simple but there were still challenges around the order of operations of applications and the reliance of a run book which inevitably brings in the possibility of human error. Zerto is truly a game changer when it comes to tools that help organizations tackle the challenge of DR.

Brief history

Zerto is an Israel based company. It was founded by Ziv and Oded Kedem who also found Kashya back in 2000. When Kashya was introduced it too was a game changer when it came to DR and data protection. Back then DR was a very manual process and SAN replication was the tool used to replicate data between a primary and secondary sites. The challenge with SAN replication that its typically expensive, complex to implement and was dependent on hardware. Kashya moved replication to the host or switch level (depending on the solution) using a product called Cisco SANTap. Not only did it just mirrored data but it brought continuous data protection or CDP to the table. For everything that Kashya brought it still didn’t address complexity and management challenges with the overall solution.

In 2006 EMC purchased Kashya and it became EMC RecoverPoint. After selling the company both Ziv and Oded started a new project called Zerto. Zerto addressed some of the challenges that Kashya had by moving the replication engine from the SAN to the hypervisor. With replication taking place at the hypervisor level simplified the overall installation of Zerto. There are no additional hardware components or overly complex configurations on the SAN. It was software only appliance that was purpose built for virtual environments. Zerto also addressed some of the shortcomings around another product called VMware’s Site Recovery Manager or SRM. With replication taking place at the hypervisor level made it easy for Ziv and Oded to add DR automation and orchestration to make Zerto a complete DR solution.

How does Zerto work?

Zerto needs a Virtual Replication Appliance or VRA installed on each ESX or virtual hosts in the environment. The VRA is a Virtual Appliance running a form of Linux Debian. The VRA splits incoming IO through the virtual SCSI stack using a IOVP (I/O Vendor Partner Package) driver that resides on each host. This gives it more direct access to the IO than VMware vStorage APIs and change block tracking which is used by a lot of backup software. Zerto uses asynchronous replication.

Replication supports WAN compression and throttling automatically and its intelligent enough to detect changes in the link and rollback any actions that didn’t complete at the other side. A nice feature those who have limited bandwidth or don’t want to congest the WAN

Zerto doesn’t leverage snapshot technology like a lot of replication technologies but instead uses journaling. The journal holds all data changes which allows you to rollback to a specific point in time. This gives you low RPO (Recovery Point Objectives) which can’t be achieved by snapshot based technologies. Journaling is effective and can deliver tight RPOs but does come with some caveats. The longer you want to go back the larger the journal needs to be in order to accommodate those requests. The same goes for IO intensive applications. If there is a high rate of data change then you will need adequate journal space to accommodate. So size accordingly and have reasonable requirements.


The Zerto Virtual Manager or ZVM is a small piece of Windows software that can be installed on vCenter or in SCVMM server. The ZVM’s job is to monitor replication, define Virtual Protection Group or VPGs (We’ll get to that later) and ultimately protect VMs. This is in contract to the VRA which sole job is to split IO and replicate data. It’s recommended that you have 1 vCenter or SCVMM server per data center so that if in the event of a disaster you can failover your site. Both servers should be protected to prevent downtime. If vCenter of SCVMM server is down not only can’t you manage your virtual environment but the ZVM will be unavailable as well. ZVM needs to communicate with the ZVM over TCP port 4005. Make sure that this port is open on any firewall between your production and DR sites. The Zerto Virtual Manager can be accessed by via port 9080 and the GUI is HTML 6.

DR Automation and Orchestration

Zerto uses a Virtual Protection Group or VPG to protect Virtual Machines. A VPG is typically used on a per application basis. It provides Virtual Machine consistency groups, define RPO, CDP history, and WAN optimization and compression, failover configuration, and boot order which defines the order the Virtual Machines come up. The VPG is where you can put your DR plan to work. With properly configured VPGs you have a working DR plan for your virtual environment which help drive down RTO (Recovery Time Objective).

Zerto also allows for the ability to do point-in-time DR testing non-disruptively without impacting replication or the production environment. This is a great way to test your environment on a regular basis without having to deal with the outages and/or after hours work. Note: This doesn’t replace the need perform actual test. I always recommend that organization test their BCDR plan once a year at a minimum.


In conclusion, Zerto brings the replication and DR automation to the SMB and Enterprise customer. It is simple to deploy, configure and administer which gives it an advantage over more complex solutions like VMware SRM and storage array based replication. In addition, it a tool that has become storage and hypervisor agnostic taking the dependence on the hardware and hypervisor out of the equation. Allowing customers to make more economical decision when evaluating a DR strategy.

It should be noted that Zerto doesn’t replace the need for a good Business Continuity and Disaster Recovery Plan. I have seen some people think that a product like Zerto will just magically create a DR plan for their environment. For all the cool things it does it can’t understand business and create an effective DR plan. Zerto is only a tool that helps put that plan and makes its actionable. In a future blog post I’ll talk more about Business Continuity and DR planning.