Do you have storage? Do you stretch your vSphere over distance? Then you’ve probably talked to your EMC rep about VPLEX and running vSphere with VPLEX Continuous Availability. In fact, you probably use VPLEX to stretch your vSphere cluster between two datacenters. And lately, you may have heard about VMware’s own solution to this problem, Virtual SAN (VSAN) Stretched Clustering.
Since VSAN Stretched Clustering was released in August of 2015, we have seen a steady chain of questions asking about the key differences between VPLEX Metro and VSAN Stretched Clustering. I thought it would be helpful to call out the main differences and similarities here, in a central location, for everyone to see. Nothing to hide here folks!
The most important point to cover, right from the start, is that VSAN Stretched Clustering is a great solution for running vSphere Metro Storage Cluster (vMSC) between two datacenters! It absolutely works, and does exactly what you need it to do. VSAN’s stretched solution allows you to use VMware High Availability (HA), Dynamic Resource Scheduler (DRS) and, of course, gain instant vMotion over distance, just like you get with VPLEX. It also gives you the option of running a VM-based Witness to allow for increased survivability for your VMs in the case of a site or network outage. VPLEX expert confirmed and approved!
Is it strange for a VPLEX blog to go on about VMware’s awesome VSAN Stretched Clustering solution? Not really. Has this author completely lost his mind? Not relevant. I can focus on the excellence of the VSAN solution simply because VSAN and VPLEX don’t really compete. In truth, VSAN and VPLEX provide many of the same benefits but target separate customers. It all comes down to this. With VSAN a customer must use all direct-attach storage, and with VPLEX all the storage must come from supported storage arrays behind VPLEX.
This really is the major difference to the customer between the two. Is your storage on your vSphere servers, or do you have a Storage Area Network (SAN)?
There are other differences, of course, that are less glaring and less impactful. VPLEX supports connectivity between sites using either Fibre Channel (FC) or Internet Protocol (IP), while VSAN is only IP based. Even within the support of IP connectivity there are differences in the recommended minimum setups between VPLEX and VSAN: 3Gbps vs 10Gbps, up to 10ms RTT vs 5ms RTT, layer 2 or 3 connectivity vs layer 2 only. Finally, there is the fact that, although the new Fault Tolerance (SMP-FT) is not supported in any vMSC environments, VPLEX does support using the older RR-FT for automatic FT recovery of VMs between sites; VSAN does not.
As I’ve said, all of these are minor compared to the major point of leveraging your existing storage infrastructure. Being able to use XtremIO for VDI, or VMAX for mission critical databases, Unity, or even non-EMC arrays means better performance and higher availability for your VM environment. As soon as you bring SAN storage into the discussion, VPLEX allows you to take advantage of your existing investments and enables the use of targeted best-of-breed technology.
While VSAN and VPLEX can provide the same benefits and cover the same use case of stretching your VMware cluster between two datacenters, with all the benefits an Active/Active solution provides, if you have any existing storage arrays VPLEX is your only choice between the two. VPLEX Metro is trusted by thousands of customers to provide Continuous Availability for VMware vSphere clusters. The arrival of VSAN Stretched Clustering doesn’t change that trust. Pick the option that best fits your environment, and be happy with the knowledge that your vSphere environment and your VMs have been given Metro superpowers!