I have noticed an increasing number of VMware installations using some form of VSAN. The core concept of a virtual SAN is to utilise in local discs per VMware host and then create a shared volume of the discs across all hosts.
The discs are placed back into the servers and become local, and we can mix SSD and spinning rust to create hybrid storage with the SSDâ€™s providing caching.
This is all done via the hypervisor kernel and no other physical appliances are required. Everything is performed in software.
I think this is what the term â€œHyper convergedâ€ refers to.
VMware VSAN is a licensed feature which you add to your cluster, Every node/CPU in your cluster requires to carry a license. There is also a Hardware Compatibility List (HCL) for the components which you place into the servers.
I do not understand the point of this myself, I see more downsides than advantages.
â€¢ Every node contributes storage to the cluster, over a VSAN (10 gig recommended) network. Every time you take a node into maintenance, you have lost redundancy and IO.
â€¢ Itâ€™s an additional service sitting in the ESXI kernel, are we moving back to a fat ESX full blown kernel. With a SAN I have controllers with Hardware acceleration VAAI
â€¢ To manage my discâ€™s I have to integrate/licences more software to have a single view of my discs and volumes.
â€¢ I have to pay an additional licences if all SSD drives are used.
â€¢ To scale out your Vmware hosts horizontally, in my opinion is slower than just presenting a LUN to your host from a centralised SAN.
Iâ€™m not sure what the ultimate objective is for VSAN, but I can see it being useful in development or even Disaster recovery clusters. I will be interested to hear about any real advantages that using a â€œHyper convergeredâ€ VSAN compared to a nicely designed centralised SANS with VAAI enabled, and inter SAN snapshots and replication