Hyper-Converged Infrastructure like Nutanix and VSAN versus Host Side Caching Software
One advantage that Hyper-converged infrastructure(HCI) has over SAN infrastructure is that HCI has put high speed storage back in the hosts. This is also true for Host Side Caching software. However, unlike HCI, host side caching retains the flexibility that SAN infrastructure has over HCI, of being able to do maintenance on compute and storage hardware independently of each other.
Other advantages of Host Side Caching (paired with SAN) versus Hyperconverged infrastructure are:
When using host RAM, Host Side Caching is the fastest storage on the market.
This is simply because there are no HCI solutions on the market that are capable of using large amounts of RAM in the storage IO path. And RAM is the fastest storage media there is.
Unlike HCI, when using Host Side Caching with SAN, you can do maintenance of storage and compute independently of each other.
In HCI, because the same physical server is responsible for storage and compute, doing maintenance on compute or storage requires taking down both. On the other hand, in case of Host Side Caching paired with SAN infrastructure, storage array and compute nodes (ESXi hosts) are separate, so doing maintenance on one doesn’t affect the other.
With HCI, Host failure results in degraded storage and vice-versa, hence recovery times are longer.
In HCI, because of the above reason, storage failure results in host down, thus reducing compute resources. Also, shutting down a host takes longer since all data on locally attached storage needs to be redistributed to other hosts before the host can be shutdown. This is not the case with Host Side Caching paired with SAN storage. Since in-host cache has transient data only, with the backend array still being the system of record, recovery times from storage or compute failure are as they were with SAN storage without Host Side Cache, which is one of the main advantages of SAN infrastructure over Hyperconverged. For more information on how VirtuCache handles host failure, refer this link.
Host Side Caching is plug & play software and additional hardware is not needed.
Host Side Caching can be deployed in minutes and without any maintenance mode/downtime for VMware hosts or storage. It only requires an SSD or RAM in the ESXi host. On the other hand, deploying HCI almost always requires new server hardware.
With host side caching, there is less vendor lock-in.
SAN infrastructure has less vendor lock-in than HCI because compute connects to storage using standardized protocols like iSCSI or FC, as a result a storage array or server vendor can be swapped for another. Host Side Caching doesn’t change this dynamic. On the other hand, with HCI, since vendor specific proprietary protocol is used to connect locally attached storage to ESXi (Dell Vxrail and Nutanix as examples), you are locked-in to the HCI vendor for both storage and compute. So if you want to add another Hyperconverged node, you’d need to buy it from the same HCI vendor.
Summary
Host Side Caching in some sense is the best of both the SAN and HCI worlds – it retains the advantage that SAN infrastructure has over HCI that storage and compute are independent of each other, which lets both be maintained and scaled independently, while at the same time, providing the performance advantage that HCI has over SAN array by bringing Flash closer to compute.
