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Out Of Space? Thin Provisioning Vs. Traditional Provisioning

There has been a lot written about thin provisioning and how it can optimize capacity and increase efficiency of the storage administrator. The constant response is that thin provisioning is "risky" compared with traditional hard-provisioned volumes. Is it really?

Thin provisioning was driven to market success by companies like 3PAR and Compellent and now just about every major storage vendor offers thin provisioning. The proposed fear about thin provisioning is what if you have over-subscribed your storage or have a sudden need for storage and suddenly find yourself without capacity?

When the "oh my, I'll run out of capacity" debate comes up, I always ask, how is this any different with hard provisioning? If you have a server with storage allocated to it and you suddenly run out of capacity, what are you going to do? Assuming it is on a SAN, you are going to stop what you are doing, hope that you have reserve capacity, and assign it to the LUN that had just run out of storage. After this you still need to run the OS provisioning tools so it will recognize that additional capacity. And, of course, hope it works like it should. Seems that it often does not.

What if you are out of your reserve? Or what if your reserve does not have the right type or speed of drive? The likelihood of this happening is just as high as you running out of capacity on a thin-provisioned system. Then what are you going to do? Unallocating capacity from an existing hard LUN is not easy and, in most cases, it is impossible. The manual process in moving this data is ugly; you more likely will live with it and just place a rush order for more capacity.

In fact, in this scenario, thinly provisioned volumes are safer. The reserve, if you will, on a thin volume already is shared. There is no allocation that needs to occur and no reassignment to be done. In fact, because the capacity is shared, the chance of you running out of space on any particular server is much lower than in the hard environment.

The hard-provisioning options are to either massively over-allocate your storage on a per-application basis or to manage and monitor your volumes in an almost draconian fashion. The first option is going to be expensive from a hard cost standpoint. The second will be expensive from a people allocation perspective. Neither option is very viable cast against the current economic situation.

The important thing is that managing this capacity with a storage system that supports thin volumes is automatic and in these times of stretched thin IT staffs, efficiency is critical.

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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.

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