SRM Replication-Difference & benefits between Array-based and Host-based Replication

First, let’s talk about what is SRM replication. so basically, SRM leverages VMware vSphere Replication to provide hypervisor-based virtual machine replication. It protects VMs from partial or complete site failures by copying the virtual machines from a primary site to a secondary site, or from multiple sources to a single disaster recovery site.

SRM Replication:

We can replicate virtual machines by using either array-based replication, vSphere Replication, or a combination of both. We cannot use both replication technologies to protect the same virtual machine.

 

Two Types of Replications:

1) Array Base

2) Host Base or vSphere Base

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 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. 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 can monitor and control array functions related to migrations, failovers, re-protections, failbacks and tests. SRA able to replicate powered off VMs, Templates, Linked Clones and ISOs. 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.

 

 

vSphere or host-based Replication:

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. 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.

 

 

 

Difference & benefits between Array-based and Host-based Replication in SRM:

 

The following table lists the differences & benefits between the two replication technologies

              

Characteristics	Array-Based Replication	vSphere Replication
Type	Replication using the storage layer.	Replication using the host or vSphere layer.
Recovery point objective min or max	0 up to max supported by vendor.	5 minutes to 24 hours.
Scale	Scales up to 5,000 VMs protected, 2,000 simultaneously recoverable through vCenter and Site Recovery Manager pairing.	Scales up to 2000 VMs (protected and recoverable) through vCenter and Site Recovery Manager pairing.
Write-order fidelity	Supports write-order fidelity within and across multiple VMs in the same consistency group.	Supports write-order fidelity on the disks or VMDKs that comprise a VM. Consistency cannot be guaranteed across multiple VMs.
Replication level	Replicates at the LUN, VMFS, or NFS volume level.	Replicates at the VM level.
Replication configuration	Replication is configured and managed on the storage array.	Replication is configured and managed in the vSphere Web Client.
Array and vendor types	Requires same storage replication solution at both sites, for example, EMC RecoverPoint, NetApp vFiler, IBM SVC.	Can support any storage solution at either end including local storage if it is covered by the vSphere HCL.
Storage supported	Replication supported on FC, iSCSI, or NFS storage only.	Supports replicating VMs on local, attached, Virtual SAN, FC, iSCSI, or NFS storage.
Cost	Replication and snapshot licensing is required.	vSphere Replication is included in vSphere Essentials Plus Kit version 5.1 and later.
Deployment	Deployment is fairly involved and must include storage administration and possibly networking.	Deployment requirements are minimal: OVF at each site and start configuring replications.
Application consistency	Depending on the array, application consistency might be supported with the addition of agents to the VM.	Supports Volume Shadow Copy Service and Linux file system application consistency.
Fault Tolerance (FT) VMs	Can replicate UP FT-protected VMs. After a VM is recovered, it is no longer FT enabled. Does not support FT VMs that are configured for SMP.	Cannot replicate FT-protected VMs.
Powered off VMs, templates, linked clones, or ISOs	Can replicate powered off VMs,templates, and linked clones, if all nodes in the snapshot tree are also replicated, and ISOs.	Can replicate only powered on VMs. Cannot replicate powered off VMs, templates, linked clones, ISOs, or any non-VM files.
Raw device mapping (RDM) support	Physical and virtual mode RDMs can be replicated.	Only virtual mode RDMs can be replicated.
Microsoft Cluster Service (MSCS) support	VMs that are part of a MSCS cluster can be replicated.	Cannot replicate VMs that are part of an MSCS cluster. vSphere Replication cannot replicate disks in multiwriter mode.
vApp support	Replicating vApps is supported.	You cannot replicate vApps. You can replicate VMs that are part of a vApp and create a vApp at the recovery site that they are recovered to.
vSphere versions supported	Hosts running vSphere 3.5 through 6.x are supported.	Hosts must be running vSphere 5.0 or later.
Multiple point-in-time (MPIT) snapshots	MPIT snapshots or rollback is supported by some supported array vendors, for example, EMC RecoverPoint	Supports up to 24 recovery points.
Snapshots	Supports replicating VMs with snapshots and maintaining the snapshot tree.	Supports replicating VMs with snapshots. However, the tree is collapsed at the target site.
Response to host failure	Replication is not impacted.	Host failure and the VM restarting on another host trigger a full sync.