SRM supports two different replication technologies, Storage Array or Array-Based Replication and vSphere Replication. One of the key decisions when implementing SRM is which technology to use and for what VMs. The two technologies can be used together in an SRM environment though not to protect the same VM. Given that, what are the differences and why would you use one over the other? This table will provide all the answers you need:
| Array-Based Replication | vSphere Replication | |
| Type | Replication using the storage layer | Replication using the host/vSphere layer |
| RPO min/max | 0 up to max supported by vendor | 5 mins to 24 hours |
| Scale | Scales up to 5,000 VMs protected/2,000 simultaneously recoverable per vCenter/SRM pair | Scales up to 2,000 VMs (protected & recoverable) per vCenter/SRM pair |
| Write order fidelity | Supports write order fidelity within and across multiple VMs in the same consistency group | Supports write order fidelity on the disks/VMDKs that make up 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/ vendor types | Requires same storage replication solution at both sites (eg. EMC RecoverPoint, NetApp vFiler, IBM SVC, etc) | Can support any storage solution at either end including local storage as long as it is covered by the vSphere HCL |
| Storage supported | Replication supported on FC, iSCSI or NFS storage only | Supports replicating VMs on local, attached, VSAN, FC, iSCSI or NFS storage |
| Cost | Replication and snapshot licensing is required | vSphere Replication is included in vSphere Essentials Plus 5.1 and higher |
| 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 may be supported with the addition of agents to the VM | Supports VSS & Linux file system application consistency |
| FT VMs | Can replicate UP FT protected VMs (once recovered VM is no longer FT enabled). Does not support SMP FT VMs. | Cannot replicate FT protected VMs |
| Powered off VMs/Templates/Linked clones/ISO’s | Able to replicate powered off VMs, Templates, Linked Clones (as long as all nodes in the snapshot tree are replicated as well) and ISOs | Can only replicate powered on VMs. Cannot replicate powered off VMs, Templates, Linked Clones, ISOs or any non-VM files |
| RDM support | Physical and Virtual mode RDMs can be replicated | Only Virtual mode RDMs can be replicated |
| MSCS support | VMs that are part of a MSCS cluster can be replicated | Cannot replicate VMs that are part of a MSCS cluster. VR cannot replicate disks in multi-writer mode. |
| vApp support | Replicating vApps is supported | Replicating vApps is not possible. However, it is possible to replicate VMs that are part of a vApp and to create a vApp at the recovery site that they are recovered into |
| vSphere versions supported | Hosts running vSphere 3.5-6.5 are supported | Hosts must be running vSphere 5.0 or higher |
| MPIT | Multiple point in time snapshots or rollback is supported by some supported array vendors (eg. 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 triggers a full sync. For details about what a full sync involves see the vSphere Replication FAQ |
If you want more information on supported array-based replication vendors and compatibility check out the VMware Compatibility Guide. The vendor for the array you have or are interested in is also a great source for information. Reading the release notes for your SRA is highly recommended.
For detailed information on vSphere Replication including answers to commonly asked questions check out the vSphere Replication FAQ
