From a hardware perspective, you will need at least 3 ESXi hosts. You will also need at least one HDDs (magnetic disks) per host and at least one (SSDs) Solid State Disks per host. At least 3 ESXi hosts in the VSAN cluster must contribute local storage to the vsanDatastore, and this local storage must be a combination of SSD and HDD. There are a couple of best practices to call out here:
- VMware recommends that there is at least a 1:10 ratio of SSD:HDD. Depending on the working sets of your virtual machines, you may need to make this ratio higher.
- While VSAN can scale out on compute only, i.e. a subset of ESXi hosts providing compute and storage and additional ESXi hosts providing compute only, VMware recommends as a best practice that all hosts in the VSAN cluster be configured similarly if not identically from a storage and compute perspective.
With that in mind, the choice of SSD is essential to VSAN performance. VMware is providing a HCL which will grade SSDs on performance. Obviously the higher the performance (number of sustained write operations per second), the better the performance of your virtual machines and the higher the density of virtual machines per host. However, lower grade SSDs will work just fine, on the understanding that your VM density will be lower. It should also be noted that a number of PCIe based SSDs are also supported. Another consideration when choosing SSDs should be the longevity or lifetime guarantee that comes with the SSD. Choose your SSD carefully.
The next item to highlight is the disk controller. VSAN implements a distributed RAID configuration across all hosts in the cluster. This means that if a node fails (taking its local storage with it of course), virtual machines still have a full complement of data objects available and can continue to run (very much like RAIN – Redundant Array of Independent Nodes). How is this related to the disk controller you might ask? Well, the disk controller needs to be able to run in pass-thru mode or HBA mode; this allows the physical disks to be passed directly through to the ESXi host without a layer of RAID on top. VSAN will take care of the RAID requirements. Again, the HCL should be referenced for further details on supported controllers that work in pass-thru/HBA mode.
Finally, your network needs to be considered. VMware is supporting both 1Gb and 10Gb network interconnect between ESXi hosts. VSAN requires that a VMkernel port is configured to carry VSAN traffic between hosts. Again, although we will support both, 10Gb would be a recommended best practice for production environments. But, for the initial beta (see http://vsanbeta.com), either will suffice. If you do go with the 1Gb, then you need to keep this in mind when measuring VSAN performance, as the network may be the bottleneck if you deploy a large VSAN cluster and lots of virtual machines with policy settings that generate a lot of VSAN network traffic.
That’s it – with these requirements met, you are good to go with VSAN. To see some demos on VSAN, and steps on how to configure it, check out these online product walk-throughs here.