Tag Archives: Srm

Differences between VMware Site Recovery Manager vs Zerto Replication

Disaster recovery is critical for any business. With virtualization technology disaster recovery has become simpler and easier to implement. One of the most common ways to implement disaster recovery is replication – where a specific segment or an entire production footprint is replicated to a disaster recovery site.

Here we will briefly discuss and compare two of the most commonly used replication software that are widely used in the industry today.  VMware’s Site Recovery Manager(SRM) and Zerto Replication Software are two of the most commonly used replication technologies that allow you to protect your production footprint.

VMware’s Site Recovery Manager (SRM) and Zerto replication are both disaster recovery management and orchestration solution that provide disaster recovery by means of replication. While SRM is a product that is developed by VMware, Zerto software is a product of Zerto technologies. Both use vSphere’s API to integrate into vCenter and manage replication.

We will compare both technologies on these three factors – features, functional components and replication technology. This will allow you to get an overall idea of what is involved in deploying these two products in your infrastructure and determining which one is a better fit based on your use case.

Features – Below is a comparison of the feature set between VMware’s SRM and Zerto replication.

  VMware Site Recovery Manager Zerto Replication
Total number of virtual machines configured for protection per vCenter 5000 5000
Total number of virtual machines protected per appliance 500 (with vSphere replication) 500
RPO <15 minutes (Storage replication), 15 minutes (vSphere replication) <15 minutes
Ability to work with Storage replication Yes No
Virtual machine consistency groups Yes Yes
vSphere Client Integration Yes Yes
RDM Support Yes (Virtual RDM only) Yes
RE-IP of Virtual Machines Yes Yes
API support Yes (SDK) Yes (RestAPI)
Licensing Per-VM Per-VM
Post-Script Execution Yes Yes

Functional Components

Below is the architecture of SRM.

srm1

We will break down the parts and describe them below,

Site recovery Manager – This is the SRM software that manages and orchestrates the entire solution and is critical for being able to manage a disaster failover. The software is installed on a Windows server and can be installed in a virtual machine. The SRM server is configured to connect to the vCenter server on each site.

Once the connection is done, site pairing is done between both sides allowing each site to be able to access the other site and resources are mapped.

VM Replication – SRM has the ability to support replication by means of virtual machine replication. This is done by deploying VR appliance at each of the vCenter and VR agents on each of the hypervisors. The agents are able to track and ship blocks of traffic across the WAN through the VR appliance that are received on the other site. The benefit of VM replication is that it is storage agnostic and can replicate regardless of the backend storage used.

Storage Array Replication – One of the most common modes of replication seen while using SRM is storage array replication. In this scenario, the storage array itself handles the replication while SRM orchestrate a DR event by directly communicating with the storage. This is done by deploying Storage replication adapter (SRA) on the SRM server that communicates with the storage array directly. SRM is able to send commands via this SRA to the storage array to break replication when a DR event is triggered.

Below is the architecture of Zerto –

zerto1

Zerto Virtual Manager (ZVM) – ZVM is deployed on a Windows virtual machine and runs as a service that manages replication between the production and the recovery site. The ZVM is configured to tie into the vCenter server on each site respectively.

Virtual Replication Appliances (VRAs) – Virtual replication appliances are virtual machines installed on each host being managed by a vCenter that have virtual machines that need to be protected. The VRA manages the replication data that is being replicated to or from a protected site.

Zerto User Interface – The replication is managed by the user interface via the Zerto user interface. This web interface is accessible both via the vCenter client or the vSphere web client.

Replication Technology

VMware’s SRM and Zerto both have the ability to perform virtual machine replication however SRM has an additional functionality of being able to offload the replication to be managed by the storage array.

Being able to offload the replication to the storage array comes with its own benefits and some drawbacks as well.

One benefit of replicating using the storage array is the low RPO that the storage array is able to offer. Array replication is considered to be more efficient in the sense that the arrays offer efficient ways of data management and transfer.

Array replication on the other hand requires similar storage arrays on both sides and additional licensing for replication – both being very expensive. This also requires multiple teams to be involved in getting the entire setup complete – this can cause management problems while architecting or executing a DR plan.

Zerto replication replicates by means of virtual machines replication only. Zerto manages and replicates by means of the Zerto Virtual Manager (ZVM) that connects to a vCenter. The ZVM also deploys the Virtual replication appliances (VRA) on to each vSphere host that is participating in replication. This VRA is able to watch all writes being sent to virtual machines and is able to make a copy and ship these writes across to the other site, there by achieving RPO in seconds.

As soon as a write is seen by the VRA it quickly copies it over and sends it to the ZVM that transports the write to the other side.

Conclusion

SRM and Zerto are both efficient enterprise class replication software that make it easy to deploy, manage and execute a disaster recovery run book. Both software can be easily deployed and integrate seamlessly in the vSphere client and vSphere web client. While SRM can be a great fit for a mixed tier replication i.e. storage and virtual machine replication, zerto can be targeted towards small and medium business foot prints that allow for cost savings by not having to purchase expensive storage infrastructure.

INTERESTING PAPER ABOUT DISASTER RECOVERY ON VCLOUD DIRECTOR

I ran into this paper which explains how to have DR setup for your vCloud director foot print using SRM.

This is for vCloud Director 5.1 but most of the concepts are still the same and apply for vCloud Director 5.5.

Let me know what you think 🙂 and here’s the link!

RE-REGISTER SRM vCENTER SERVER EXTENSION

Long story short – our vcenter server crapped out for some reason. I won’t go into those details because it seemed like a trivial issue however this vcenter was also associated with the SRM server.

After the vcenter server was back up – the fix was a clean re-install 🙂  – the SRM service went offline and failed to come back up. The event logs were not specific but the fix for that was running through the ODBC connection setup again. This certainly seems like a known bug to me.

However I was confused about how to re-register the vCenter server extension for SRM. I tried to reinstall the extension but it would not show in the plugins drop down. Typically, if the vcenter server is still the same server – and in this case it was since I reinstalled it – the SRM plugin should show up in the drop down however it did not. The fix was easier than ever.

When the SRM installation is complete, ensure that vCenter Server is registered in the extension.xml configuration file.
 
To ensure that vCenter Server is registered in the extension.xml file:
  1. Browse to the SRM configuration folder at C:\Program Files\VMware\VMware Site Recovery Manager\config.
  2. If the vCenter Server address is incorrect, update the correct address using the command: 

    srm-config -cmd updateext -cfg ../config/vmware-dr.xml -extcfg ../config/extension.xml

Hope this helps. The vmware KB article is here.

Feel free to comment or correct me 🙂