In this series of SRM we will see about Site Recovery Manager. In previous post we have looked at the SRM Overview. In this post we will see on Replication Options in the SRM. SRM basically supports 2 types of replication vSphere based replication and Array Based Replication. For vSphere based replication you require an VMware vSphere Replication Appliance where as in Array Based Replication you will require Replication Adapters from storage vendor. This is the second post of the SRM Series so if you have missed the first post make sure to check link at the end of this post. It will help you to understand about SRM.
Replication is used to replicate the virtual machines from one site to another site For example you can say DC site to DR site. SRM can be used with either vSphere Replication or the Array based replication. One virtual machine can not be replicated by both. If you want to use the SRM then first you should configure the replication technology for the virtual machine, so you can make do Disaster recovery , Planned migration testing on the virtual machine. In this post we will discuss more about both the replication technologies. So you can make decision which replication option you want to go for your environment.
First we will see about the Array Based Replication then we will see on vSphere Replication.
Array Based Replication:
Array based replication works at the storage level that means directly storage is replicated to the another site instead of the individual virtual machines. SRM requires same storage solution at both the sites. Below is the image of the Array-Based Replication taken from VMware Docs. Which will help you to understand how it works.
Array Based Replication require the SRA (Storage Replication Adapter). SRA must be installed at both the sites in the SRM Server, as you can see in the above image. SRA is an small software provided by the storage vendor and must be compatible with VMware vSphere for use. SRA is an component which is installed with the SRM in the windows server, which is used for communicating with storage arrays. They are therefore installed on the Site Recovery Manager servers at both sites and are able to monitor and control array functions related to migrations, failovers, re-protections, failbacks and tests.
SRA able to replicate powered off VMs, Templates, Linked Clones (as long as all nodes in the snapshot tree are replicated as well) and ISOs. If you are using RDM then Physical and Virtual mode RDMs can be replicated using Array-based replication.
SRA replicates the LUN/VMFS and the NFS Level. So your storage volume or datastore will be replicated directly. It is supported on FC, iSCSI and NFS only. You may require additional licensing cost for the replication and snapshot feature for the storage arrays. Before going with the Array based replication check for the features provided and the VMware vSphere Compatibility so you don’t face any issues later.
vSphere Replication uses vSphere Replication appliance, which provides individual VM Replication as compared to direct storage replication. So you can configure replication on per VM Basis. Below is the image of the vSphere Replication taken from VMware Docs. Which will help you to understand how it works.
For using vSphere Replication first you need to Deploy and Configure vSphere Replication Appliance. vSphere replication provides the individual VM based replication. So you can configure replication only for your critical VMs. vSphere Replication supports any storage as long as storage is supported by VMware. There is no requirement of similar storage at both the sites.
vSphere Replication provides RPOs as low as 5 minutes. vSphere Replication can only replicate powered on VMs. Cannot replicate powered off VMs, Templates, Linked Clones, ISOs or any non-VM files. If you are using RDM then only Virtual mode RDMs can be replicated. vSphere Replication does not require additional licensing cost.
There may be many features which are there in Array-based Replication but not in vSphere Replication and vice versa. So check for the VMware HCL, Features comparison before making decision so you can choose the replication based on your requirement.
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Image Credits: VMware Docs.
Reference: VMware SRM Technical Overview.