VMware VSAN is a cool technology and probably something you already heard of (100% if you constantly follow my blog). As there are a huge amount of information available on the internet I decided to strap them down a bit and focus on the key aspects in form of a FAQ. This blog post is not meant to give you any special technical information about how to configure or use any VSAN component but rather gives the VSAN newbies a quick overview what VSAN is, what it does and if it fits for you.
What is VSAN?
VSAN is the software defined storqage component from VMware to complete their vison of a software defined datacenter
How long is VSAN available
Version 1.0 was published in March 2014 after a two-year beta program. Current version is 6.1 but the naming convention was changed after VSAN 2.0 that came with vSphere 6 to match the vSphere release number. So VSAN 6.1 is actually the third major version of VSAN since initial release
Is VSAN a separate product and where can I get it?
VSAN functionality is build in the ESX kernel. So everyone who uses vSphere 5.5 and above already has VSAN. There is no separate download for the product. The management is fully buil-in vCenter/web client (not the c# client)
Can I use VSAN to provide storage for non-VMware hosts?
No, VSAN is an ESX-kernel inbuild storage solution that uses a proprietary protocol for communication. Only ESX is able to understand and use this protocol.
How does VSAN work?
VSAN uses direct-attached disks from each participating node. A storage node has to contribute a minimum of one SSD and one magnetic disk configured in one disk group. VSAN uses flash for read and write cache and the magnetic disks for the data (capacity tier). Each storage node can have a maximum of 5 disk groups each containing one SSD and up to 6 magnetic disks. That way each node can have a maximum of 5 SSDs and 30 magnetic disks.
The maxmimum number of VSAN nodes in one single cluster is 64 nodes (this is rather a HA limit and not a VSAN limit)
Beside the hyprid configuration where SSDs and magnetic disks are used together, there is also an All-Flash version that uses flash for cache and capacity.
Cross-node communication is done over Ethernet networks over multicast. 1GbE is the minimum for hybrid setups, for all-flash you need 10GbE. The "mirror" links can be routed over L2 or L3 networks.
VSAN is a scale-out product, so scalablity is given by adding more storage nodes to the cluster.
How is VSAN licensed?
At the moment VSAN is licensed primarly the same way as ESX is. There is a per-socket license available at ~2800€/socket (plus support) for the hybrid setup. If you want to use all-flash then you have to buy the add-on for ~1300€ per socket, so ~4100€ per socket in sum.
Each node using VSAN storage has to be licensed no matter if it contributes storage to the cluster or not.
How to configure VSAN on the hardware side?
There are currently two ways to configure your VSAN hardware. First is build-your-own, second is to use VSAN ready nodes. Build-your-own has the advantage of being flexibel regarding performance and capacity per node. All you have to do is to follow the design guides from VMware and only use hardware from the HCL. This si especially true for the SAS controllers and the SSDs. Ignoring this HCL can led to poor performance and stability issues. Regarding to VMware support, 80% of all VSAN calls are related to hardware used that is not on the HCL. This is that important that VMware build a health check plugin taht checks all your hardware against the latest HCL and tells you whenever you use uncertified hardware or old driver versions.
Second is to use VSAN ready nodes. Nearly all major hardware vendors offer these preconfigured models that are no more than standard servers with only certified hardware build into them. The advantage ist that you won't have to care about the HCL yourself, the vendor will do it for you. To be comparable VMware introduced the "series" modelling for the VSAN ready nodes. The serie will tell you what maximum performance and storage capacity per node you can expect. There are currently 6 series - the hybrid path offers HY-2,4,6 and 8, the all-flash path offers AF-6 and 8. The disadvantage is that is not supported to upgrade a ready node later.
What are configuration minimums?
- At least 3 nodes for a non-ROBO environment but it is strongly recommended to have at least 4 nodes so one one can fail and still the whole cluster is in fully redundant mode
- At least 2 nodes in a ROBO environment and a third "virtual ESXi" whitness instance somewhere outside this two node cluster (available with VSAN 6.1 and above)
- 1 SSD and 1 magentic disk (hybrid) or 2 SSDs (all-flash) per storage node
- 1GbE network connectivity exclusively for VSAN traffic for hybrid configurations and 10GbE for all-flash
- vCenter Server and WebClient
What are the key features of VSAN?
How to size VSAN?
There are two good ways. First is to use the tools and knowledge of your choosen partner. He will size the solution for you. This is a good way if your environment you want to put on VSAN isn't completely virtualized using VMware vSphere. You can also do the sizing on your own but that's only for expert users because SAN can be complex to understand and to be monitored.
If you already are on vSphere and just want to replace your existing storage you can go to a VMware partner. He is able to do an assessment with VMware-provided VSAN tools that will check your environment and collects important performance data and statistics from your current setup. This way a sizing will be much more accurate. As a result you will get a sizing based on ready-nodes or, if you want to be more flexible, on a build-your-own solution.
How to patch/upgrade?
VSAN is patched and upgraded by updating the ESXi kernel version via Update Manager.
Interoperability with other VMware products?
VSAN is fully integrated into vSphere as already mentioned several times in this article. Other integrations are available for vRealize Operations and LogInsight.
How to monitor performance?
Currently there are two ways to monitor the performance of VSAN. First is to use VSOM and the VSAN plugin. This will give you a quite decent view into what VSAN does and how it performs.
If you need more details or better said a really deep-dive into every single counter VSAN offers, you can use VSAN observer. This tool is currently Ruby-based and has to be started from the command line. It will spawn a tiny webserver that transforms the data it collects to nice graphs. Interpreting the data can be hard and VSAN observer is primarily build for the VMware support but if you want to feel free to use it.
What to expect from future versions?
VSAN is a focus product of VMware so new features will probably come with new versions in a shorter timeframe. Especially the stretched cluster features offers some improvement chances. Additionally VMware has a strong commitment to the "ease of use". The technology behind VSAN is complex but the use of VSAN is easy and user friendly. And it's getting easier with every new version. E.g. VMware is about to implement performance counters into the web client to have a single pane of glass for all important information.