Comparison: Zerto vs. Site Recovery Manager (SRM) & vSphere Replication

Comparison: Zerto vs. Site Recovery Manager (SRM) & vSphere Replication

Comparison: Zerto vs. Site Recovery Manager (SRM) & vSphere Replication

Virtualization has made disaster recovery tremendously less complex for companies, large and small. In fact, it’s not a stretch to say that virtualization has made disaster recovery “possible” at many companies, simply because prior to virtualization it was technically overwhelming and financially prohibitive. Thanks to the containerization of servers that makes them hardware independent and the ability to track changed blocks of those virtual machines, VMs can easily be replicated to another site, run on dissimilar servers and dissimilar storage, and then restarted at the push of a button. Never before has disaster recovery been easier. However, you still need some tools to automate it and replicate the data. After all, DR isn’t just “built into the hypervisor”.

What About Replication?

Let’s start with getting your data (your virtual machines that contain your OS, applications, and data) from the primary datacenter to the secondary datacenter. Replication is what moves them from “point A to point B” but there are various ways to do it. Yes, you should still have those VMs backed-up and stored offsite, even if you are using replication. When considering disaster recovery tools for vSphere infrastructures, many admins have heard of VMware’s Site Recovery Manager (SRM), which helps you to create, test, and execute vSphere recovery plans. However, many admins don’t know fully what SRM does and does not do. SRM isn’t an all-encompassing disaster recovery solution. SRM has always been a great solution for reviewing what VMs you have, determining what is most important, determining what is dependent on what, creating a recovery plan based on that info, testing that recovery plan, and, should the time come, executing the recovery plan. What’s missing? Actually getting the data from the primary to the secondary datacenter is not part of SRM. If there is no movement of data then the VMs aren’t actually located at the recovery/secondary datacenter and would have to be recovered from offsite backup (which could take a long time and really negates the purpose of SRM’s DR orchestration).

For a long time, replication was only available in high-end storage arrays as an add-on feature – all of which was very costly. However, with virtualization more and more software-based replication options have become available. With traditional hardware-based replication in storage-area networks (SAN) being so costly, many companies are interested in today’s lower-cost and more easily implemented software-based replication solutions.

vSphere Replication Diagram

VMware offers vSphere Replication and Zerto offers Virtual Replication – both of which are software-based replication solutions for vSphere. vSphere Replication is included with vSphere Essentials Plus and above but has a number of limitations. First off, as its name states, vSphere replication does not include all the orchestration, testing, reporting and enterprise-class DR functions that you would find in SRM. Instead, vSphere Replication replicates individual VMs within or across vSphere clusters. Certainly it is better than recovering from an offsite backup but its recovery time and scalability (even when combined with SRM) may not be enough to satisfy your needs.

Zerto is sold on a per-VM basis and is compatible with vSphere Essentials and above. Zerto’s design is unique in that it is focused on protecting your company’s applications, not just VMs or LUNs. Zerto works by running a Zerto Virtual Manager (ZVM) that ties into vCenter as a plugin and manages the replication stack and Virtual Replication Appliances (VRA), deployed by ZVM, on each vSphere host.


The VRAs can see the writes performed by virtual machines on the host and then send those changes over the network (LAN or WAN) to the ZVM secondary site. Because of Zerto’s close integration vCenter and vCloud Director, it recognizes all vCenter constructs such as folder, resource pools, virtual networks, datastore clusters, as well as vCloud Director constructs like Orgs, OrgVDCs, Org Networks, & Storage Profiles.

Zerto vs vSphere Replication (focusing around data replication):

Zerto Replication
vSphere Replication
Generally recommended for: Any size vSphere infrastructure Small infrastructures, remote offices, and non-critical applications
Max number of VMs protected per appliance and vCenter Server: 500/5000 500/500
Linked clone and template support: Yes No
Physical RDM and Virtual RDM support: Yes, virtual and physical mode RDMs are supported No/Yes, Physical RDMs are not supported but virtual RDM are supported
RPO range: Seconds 15 minutes to 24 hours
Application consistent?: Supports Windows VMs using VSS and Linux with Application Quesicense Only with Windows VMs using VSS
How VMs are chosen: VMs can be organized into Virtual Protection Groups VMs can be selected individually or multi-select but virtual protection grouping is not available
Automated failback support: Yes No, VMware recommends SRM
Allows you to plan, test, and automate failover and failback: Yes No, VMware recommends SRM
Compression included: Yes No, and neither does SRM
RE-IP addressing of virtual machines: Yes No, VMware recommends SRM
Cloning of recovery sites: Yes No
Point in time recovery: Yes, up to 5 days with standard recovery, up to 1 year with extended recovery using the Offsite Backup feature Yes, up to 24 snapshots
Compatible with vApps: Yes No
vCloud Director integration: Yes No
Snapshot-based? No Yes/No, VMware says that vSR doesn’t use snapshots technology but does use a modified version of CBT, still many of the same snapshot-based limitations apply. For example, vSR uses VM snapshots at the recovery site when recovering to a different point-in-time.

What if I Add VMware’s Site Recovery Manager (SRM) to vSphere Replication?

While vSphere Replication may initially be appealing because it is included free with your edition of vSphere, most companies quickly realize that vSphere Replication lacks the DR plan design, testing, failover, and failback orchestrations that they require. Because of this, they usually consider using vSphere Replication with VMware’s Site Recovery Manager (SRM), or using SRM with array-based replication. SRM is a fully-featured disaster recovery planning, testing, and execution tool for vSphere environments. So how would Zerto compare to running SRM with vSphere Replication?

Zerto vs VMware Site Recovery Manager (focusing around automation of disaster recovery planning, testing, and automation):

SRM (with vSphere Replication)
Provides planning, testing, and execution of disaster recovery for vSphere: Yes Yes
Designed for: Zerto was designed for hypervisor-based replication AND disaster recovery orchestration SRM was designed for disaster recovery orchestration only
Licensed: Per-VM Per-VM
Replication granularity: Per-VM and/or Per- Virtual Protection Group Per-VM or multi-select but virtual protection grouping is not available
Configure consistency groups (virtual protection groups): Yes No
Replication recovery points: Yes, up to 5 days with standard recovery, up to 1 year with extended recovery using the Offsite Backup feature Yes, up to 24 snapshots
Compatibility: Zerto works with ESX 4.0 U1 and above. Zerto can replicate between different versions of vCenter. vSR works with ESX 5.x and above. SRM requires the same version of vCenter and SRM be installed at both sites.
Managed with: vSphere Client Plugin and stand-alone browser UI vSphere Client Plugin
Replication is peformed with: Zerto Hypervisor-based replication vSphere Replication

As you can see, while SRM adds capabilities around the planning, testing, and execution of a disaster recovery, it can’t overcome the replication limitations of vSphere Replication. For this reason, most companies that use SRM have opted to use array-based replication (and they are paying a pretty-penny for it). Zerto, on the other hand, requires no specific arrays at each datacenter, no array replication licenses, no storage reorganization for DR, and it supports multi-site replication at no additional cost (for a comparison between Zerto and SRM with array-based replication, see this post).