VMware announced their new product called VSAN this week at VMworld in San Francisco CA.  The VSAN is a new offering that will allow customers to provision “shared” storage by using locally direct attached disks.  Traditionally, in order to use the features like vMotion, customers had to have an external NAS or SAN device to house the virtual machines.  VMware isn’t abandoning the idea of SAN or NAS, but they now have a lower cost offering that can help smaller businesses get more out of their capital investment.  Consider disaster recovery scenarios where a company might not want to spend the upfront cost of a SAN that may never (hopefully) be used.  This will allow a basic DR plan with less cost.

VSAN has several requirements to get started.

–          3 or more hosts

–          Each host has 1 or more SSDs and 1 spinning disk

–          A pass through Raid controller

–          A dedicated 1 Gbps Network card (10 Gbps preferred)

–          A dedicated network for VSAN traffic (similar to vMotion)

–          A VSAN Port Group on every host

How does it work?

VSAN uses the local disks of the servers to create an active disk, one or more passive disks depending on the number of host failures you’ve chosen to tolerate, and possibly a witness which is used for a tie-breaker.

Data is written to the Solid State Disks first where they are then used for read and write caching, and then offloaded to the spinning disks.

In order to make sure that a single host failure doesn’t destroy the virtual machine and all of the associated data along with it, it’s replicated to the passive copies over the new VSAN VMkernel port.  This port should be setup like a vMotion port and its own dedicated network.

You can see from the diagram below that all of the hosts are connected to the VSAN network in order to handle data requests.  Also notice that one of the hosts doesn’t have a copy of the data.  Not all hosts in your cluster have to participate in the VSAN if you don’t want them too.

You might be wondering what happens when I vMotion the virtual machine to a host that isn’t participating in VSAN.  Moving a virtual machine around is no problem.  The VM can still access all of the data via the VSAN Network.  In fact the location of the virtual machine does not matter with regards to VSAN.  As long as there is network connectivity the storage should still be available.

VSAN may be a new thing offering from VMware but it’s arguable that this technology has been around for a while.  Hyperconverged companies like Nutanix and Simplivity have been doing this for a while, where their solutions don’t require a dedicated SAN.

If you’d like to find out more, or sign up for the beta of vSAN visit: http://www.vmware.com/products/virtual-san/features.html