Finishing up the migration series, let's talk about how you would migrate out of a storage cloud. With public storage clouds in particular, this can be a critical issue. These services are all in their infancy. What if you pick the wrong one, how can you get your data back?Initially, migration isn't going to be a big ordeal because most early adopters of cloud storage are using the services as an area to store backups and archives, but as the comfort level of the services increases, so will the data sets. As those data sets increase, so will the importance of an exit strategy. Similar to migration issues with internal disk-based archive solutions, migration from a public cloud is going to be a challenge that is compounded by the fact that the Internet is between you and your data.

If the cloud supplier isn't using its own proprietary technology, migration could be made to another service using the same technology. For example, the cloud service provider could use a standard archive-based solution as its storage back end from one of the standard archive storage providers like Copan Systems, Permabit, or EMC, all of which have replication capabilities. You simply (assuming you negotiated this upfront) could replicate your data from one provider to another. Similar to online backup service providers that use tools like Asigra, moving to another provider is pretty straightforward.

If the public cloud supplier is using cloud storage and/or cloud storage software like those solutions from Cleversafe or ParaScale, again the ability to move data to another provider should exist -- just confirm that this capability is on the road map and that you are comfortable with the time frames.

Private storage clouds are essentially public storage clouds on your internal intranet, but because they are internal they follow much the same migration rules that we wrote about in our previous entry on disk archive migration. The challenge is that I expect a private cloud to grow in capacity much more rapidly than a public cloud. There is a higher comfort level, it is behind your firewall and access should be somewhat faster. With either a disk-based archive or a private cloud, selection is critical because as the capacity of the archive grows, migration becomes more and more challenging. With either technology look for scalability, cost efficiency, and reliability.

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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.