We discuss virtualisation and the storage strategies that can transform your disaster recovery plan.
It's amazing how things go full-circle. In the early days of computing, mainframes had centralised storage, partitions for different processes, and a number of other features that are making their way back into mainstream environments. In the 1980s and 1990s, distributed, client/server computing made its way into just about every company. Along with this multiplication of computers, servers proliferated, and organisations bought new server hardware each time a new service was required.
While buying new server hardware for each solution keeps services separated and prevents conflicts, this "server creep" can quickly get very expensive in both the initial purchase cost and in maintenance costs. The end result is frequently hardware that runs at a fraction of its capability.
Further, this scenario complicates related matters, including disaster recovery (DR). While it would be nice for a DR plan to be able to fully cover all services, this one-to-one backup strategy isn't very feasible or affordable, and many organisations choose instead to cover only critical services.
Storage technologies and server virtualisation to improve your DR strategy
It's well-known that server virtualisation products like VMware and Microsoft Virtual Server can help reduce server creep and better utilise server processing resources. But, when coupled with newer, relatively inexpensive storage resources, these server virtualisation products become a formidable combination that can keep costs low, provide a robust environment upon which your users can rely, and can have an incredibly positive impact on your DR plan.
Consider this: Suppose you purchase an iSCSI-based storage device and create the appropriate storage infrastructure, complete with full redundancy. iSCSI, when compared to Fibre Channel solutions of similar capacity, is significantly less expensive and much easier to deploy.
While iSCSI bandwidth is more limited than Fibre Channel, iSCSI's capability to use multiple data paths through MPIO (multi-path I/O) can bring iSCSI's capabilities on par with Fibre Channel in small- to medium-size deployments, potentially making it a suitable target for hosting virtual machines.
So, under this scenario, you could conceivably begin to virtualise your servers, running them directly from your SAN.
One benefit of many iSCSI SANs is their inclusion, at no additional charge, of software that replicates the contents of one array to a replicated array. Now, you can easily, and relatively inexpensively, replicate all of your data to a different location, possibly in a different building. As long as it's physically separate from the main data centre, your data should be safe from most disasters.
Now, assume that you are replicating the array on which you host virtual machines. If, in that second data centre, you create a smaller server farm with your virtual software of choice (VMware or Microsoft, generally, although there are others out there like the open-source Xen), you could run your entire operation from this more limited set of servers.
Why a limited set of servers? In your DR centre, you don't necessarily need to be at 100 percent capacity, although you could opt for one-to-one redundancy. I make this distinction only as a way to keep the cost for a DR centre lower to make it easier to justify to upper management.
On the DR centre servers, load your virtual machine software, and keep those systems available so that you can quickly attach your SAN-based virtual machines to the virtual hosts in the event of a disaster in the primary data centre. Voila! Instant DR! (Ok, maybe not instant.)
I want to be clear that I have not yet implemented this scenario in my organisation. I will be setting this up in my lab and fully testing it and will report back on exactly how I achieve the redundancy and what pitfalls I run into.
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