Starting to get this question more often, should I always use vsAN ESA, or are there reasons to go for vSAN OSA? The answer is simple, whether you should use ESA or OSA can only be answered by the most commonly used phrase in consultancy: it depends. What does it depend on? Well, your requirements and your constraints.
One thing which comes up frequently is the 25Gbps requirement from a networking perspective. I’ve seen multiple people saying that they want to use ESA but their environment is not even close to saturating 10Gbps currently, so can they use ESA with 10Gbps? No, you cannot. ESA requires 25Gbps at minimum, and the bandwidth requirement fully depends on the ESA ReadyNode configuration you select. Why? Well, with ESA there’s also a certain performance expectation, which is why there’s a bandwidth requirement. The bandwidth requirement is put in place to ensure that you can use the NVMe devices to their full potential.
With both ESA and OSA you can produce impressive performance results, the big difference between ESA and OSA is the fact that ESA does this with a single type of NVMe device across the cluster, whereas OSA uses caching devices and capacity devices. ESA has also been optimized for high performance and is better at leveraging the existing host resources to achieve those higher numbers. An example of how ESA achieves that is through multi-threading for instance. What I appreciate about ESA the most is that the stack is also optimized in terms of resource usage. By moving data services to the top of the stack, data processing (compression of encryption for example) happens at the source instead of at bottom/destination. In other words, blocks are compressed by one host, and not by two or more (depending on the selected RAID level and type). Also, data is transferred over the network compressed, which saves bandwidth etc.
Back to OSA, why would you go for the Original Storage Architecture instead of ESA? Well, like I said, if you don’t have the performance requirements that dictate the use of ESA. If you want to use vSAN File Services (not supported with ESA in 8.o), HCI Mesh etc. If you want to run a hybrid configuration. If you want to use the vSAN Standard license. Plenty of reasons to still use OSA, so please don’t assume ESA is the only option. Use what you need to achieve your desired outcome, use what fits your budget, and use what will work with your constraints and requirements.
RAUL AREVALO LUNA says
In vSAN ESA what happen when the NVMe device used for cache fails?
Duncan Epping says
There is no device for dedicated caching with ESA, data is cached (performance leg) on multiple devices always, so a failure is no issue.
With regards to 25Gbps networking. Can storage and VM traffic be split? By this I mean adding an additional 2x port NIC to an EAS Node running vSAN traffic on 25Gbps ports connected to a small 25Gbp “vSAN Fabric” And then run VM traffic over the other NIC which would be connected to the existing 10Gbps fabric?
Duncan Epping says
Sure, that is fully supported, and we have customers doing that. they have switches for vSAN and vMotion and then switches for VM traffic etc.