I was planning on playing with VSAN soon in my lab once I added an SSD to each of 3 hosts as required. VSAN requirements are pretty simple in that you need a minimum of 3 hosts each with an approved SSD (though that can be worked around somewhat) and the hosts must not be a member of any other cluster but for the Virtual SAN Cluster.
I’ve wanted to recommend this to small clients who have the need for shared, HA storage without adding the expense and infrastructure to support a true FC or iSCSI SAN. The hesitation comes down to price. An FC or iSCSI SAN might cost you around $20,000 – 30,000 on the low-end and upwards of $50,000 – 75,000 for a mid-range unit (think Equallogic PS series fully populated with large 15k SAS drives, blah blah). So, if you can leverage the storage in each host as Virtual SAN storage, then that should be a pretty good deal. However, once you start adding it up, the price of 3 hosts licensed for vSphere Standard and VSAN is $28,000+. You want the features of vSphere Enterprise? That’ll be $41,888. Not enough for ya? vSphere Enterprise Plus will set you back a healthy $47,000.
You might think “Well, hey, I can get a VSAN setup for $28,000 which is not too much more than base Equallogic setup and some disks” and while you’d be right, what you’re forgetting is that you still need to stack some storage inside the three hosts. So, considering you need an SSD plus some amount of SAS drives per host, you can really rack up expense per host. Additionally, VSAN requires some amount of memory for the disk group configuration and VMware recommends no less than 32GB of RAM. So, these hosts won’t be cheap on a per unit basis.
Wouldn’t it be nice if you could get away with only 2 hosts? I mean, vSphere High-Availability (HA) can get away with 2 hosts and function as a cluster – why can’t VSAN? Well, now it can! VMware has launched what they’re calling VSAN ROBO (Remote Office/Branch Office). Personally, I find that name a little bit demeaning – let’s be honest a 2-node VSAN cluster comprised of R730xd’s with SSDs and combined configuration totalling up to 24 2.5″ SAS drives could be pretty serious in the storage department. In fact, with 2.5″ 1.2TB 10k SAS drives you can get almost as much storage in an R730xd as you could an Equallogic PS4210X. Pretty impressive! So, to call that host setup a Remote Office/Branch Office solution might be doing it a little discredit. In fact, with the new 18-core CPUs and up to 768GB of RAM per host this kind of setup could run just about any SMB’s primary environment.
Anyway – the main attraction of VSAN ROBO is that it allows for a 2-host VSAN cluster. VSAN ROBO gets around the 3-host requirement by introducing a VSAN Witness Virtual Appliance. This Virtual Appliance will satisfy the role of an additional host when it comes to votes/quorum control in the cluster. You can think of this as similar to a 2-node setup in Microsoft Cluster Services that uses a file share as a third witness to assist in voting. Here are some details regarding the requirements of the VSAN Witness Virtual Appliance:
Facts and requirements of VSAN Witness Virtual Appliances:
- One witness virtual appliance is required per Virtual SAN ROBO cluster.
- The appliance does not contribute compute nor storage resources to the cluster and it is not able to host virtual machines.
- The witness virtual appliance is exclusively available and supported only for Virtual SAN Stretched Clusters and Virtual SAN ROBO edition.
- Much like the Virtual SAN Stretched Cluster, the Virtual SAN ROBO edition is only capable of supporting a single failure within the cluster (FTT=1) due to the support of only three fault domains.
- 100 Mbps connectivity (depending of the number of virtual machines this could be lower)
- 500 milliseconds latency (1000 milliseconds RTT)
- Layer 3 network connectivity without multicast to the nodes in the cluster
You can see in the above description that the Virtual Appliance won’t add into any computer or storage that exists in the cluster and is used solely as a witness. I don’t have any available VSAN ROBO pricing yet. I am not sure whether or not VMware is considering VSAN ROBO more affordable because the per-host license fee will be lower or if the affordability pivots around the fact that you only need 2 hosts. I’ll try and find out but it’s nice to see VMware building a solution for environments without 3 hosts.