One of the questions coming up in IT department meetings around the world has to do with business continuity. For those who are not familiar with the term, business continuity is defined as the ability to continue doing business despite some disaster. As example would be a company having two remote data centers; one in California and another in say New York. If an earthquake were to strike in California and send everything west of the rockies into the ocean, could the business still function with what's left in New York?
Traditionally, this kind of business continuity has been very expensive due to maintaining dual sets of equipment and other resources in two geographically different locations. Aside from the cost of replication of hardware, the bandwidth to maintain full data replication between sites is also very expensive. Usually this is accomplished using two SAN arrays at each end with array based replication. The data is written to both SANs at once, allowing business to transfer to another data center if need be. Note that there is a lot more to this process than just array based replication but I'm just trying to draw a picture for you.
With virtual infrastructure hosted on VMware servers, this process becomes a little easier and cheaper because you can have a virtual infrastructure in place at your remote location and an array that mirrors your main one. This is an excellent solution but it still adds the cost and complexity of maintaining two SANs and the respective replication between the two.
LeftHand Networks has come up with an intuitive solution for businesses wanting to have good business continuity coverage at a fraction of the cost. In a nutshell, what they have done is taken the (often surplus) internal storage on physical VMware ESX servers and chained the storage space into virtual iSCSI SANs. This means that when you cluster two or more VMware ESX servers together, you can pool their on board storage into a virtual SAN and stripe data across all the servers. This gives you the ability to fail over virtual machines AND storage in the event of a failure. What a novel idea! If you are slightly tech-y and want to look into it in more detail, head on over to LeftHand Networks home page and search for Virtual SAN Appliance for VMware ESX.