High availability vendors are addressing the rapid rise Windows virtualisation by releasing a slew of specialist solutions.

SteelEye Technology, for instance, recently announced Microsoft Hyper-V support for its DataKeeper and DataKeeper Cluster Edition solutions.

"We definitely see quite a lot of customers now beginning to put their toe in the water as to what they might put onto virtualisation," says SteelEye's EMEA director John Banfield. "We’re seeing customers who are using a virtual machine as a target for a physical machine."

Only a year ago, such customers would have had completely physical systems, reckons Banfield: "Something else that’s beginning to happen in the market place, especially with XenServer and Hyper-V coming in, is that we’re seeing more and more customers looking at having a solution that enables them to provide replication between sets of virtual machines from one set of machines to another. In that environment there may be less concern about what’s actually in the virtual machine than there is about making sure they have a real-time copy of it in the event that the main system crashes."

Such challenges should not be overstated, though, and some applications (Banfield cites SAP as an example) may not be particularly suitable for virtualised environments. Microsoft itself reckons that only about 12 % of servers are actually virtualised today. Even by 2010 or 2011, it will still only be in the region of about 24%.

"So, although it’s becoming a very pervasive technology, I think it’s easy to get too blown away by just how many physical servers there are still going to be out there operating critical applications, even in four, five years time," he says.

"We continue to see a growth in adoption of virtualisation in EMEA operations," says Andrew Barnes, senior vice president of corporate development at Neverfail which recently launched Neverfail for System Center Virtual Machine Manager.

"However, this is more the use of a virtual server to support hot-standby failover of physical servers – still – that run business-critical applications such as email. For example, a survey of our customer base over the summer told us that 78% of respondents had no plans to virtualise email servers within a year, with actually over half saying they had no plans at all. In the same survey, 64% of respondents told us they didn’t believe virtualisation on its own would meet their HA/DR needs so, clearly, there is a large market for additional software."

There is still a basic problem. Let's say you once ran Exchange, SQL Server and your business application of choice on three separate servers. And let's say you then run all three under virtualisation on just one server. If that one server goes down, you've just lost all three apps.

SteelEye's senior vice president of product management, Bob Williamson, says: "We spend a lot of time talking to prospects about what we call the 'all your eggs in one basket' problem. By putting all your applications onto a single physical server or by doing any type of consolidation onto a smaller number of physical servers, you are increasing the risk of downtime for those applications. And so what becomes very important is that you have a well thought out high availability strategy that complements your virtualisation strategy.

"So you need to make sure that you’re monitoring those physical servers where the applications are running. You also need to make sure that you’re monitoring the guest OSs running on those physical servers, so you can understand if the application itself is having any problem. So we spend a lot of time talking to our customers about the multi-tier approach to high availability when you start using virtualisation."

Double-Take Software sells the Double-Take for Virtual Systems and Double-Take for VMware Infrastructure HA solutions. EMEA MD Gerald Capon points to another challenge presented by the shiny new world of virtualisation.

"Virtualisation provides great options for local high availability, such as VMware’s VMotion solution, where virtual machines are on the same host or network and connected to a SAN," he says. "If you require multiple copies of data replication and failover, solutions like Double-Take can be more appropriate. However, the options for cross-site high availability are limited. VMware does offer its Site Recovery Manager solution but this requires SAN-to-SAN replication – not always suitable if money is an issue or you need the second site to be some distance away."

So what's the advice for IT pros looking for a HA solution for their virtualised environments?

"Primarily we’d say look at all the costs and risk points and don’t believe that virtualisation is a panacea," says Barnes. "Yes, there is potential for cost-saving due to server consolidation, but to take advantage of server-based HA this means renewing the hardware platform, implementing shared storage and sourcing rare virtualisation skills. And even when the virtual infrastructure is rolled out, solutions such as VMware VirtualCenter and VMM remain a single point of control and orchestration, and hence a single point of failure."

Capon says: "Address the business requirements; it may well be that your main objective is to improve recovery times. If, however, you want to also improve your recovery point objectives then a replication solution may be more suitable. Windows virtualisation is in its infancy but looks to offer a good alternative to VMware and should certainly be considered. Double-Take Software is already partnered with Microsoft, we demonstrated Double-Take and Hyper-V together at Tech Ed 2008 in the US, we offer a range of solutions to meet all business requirements and can even provide split-site Microsoft Clustering."