Best Practices: High hopes for thin provisioning


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It seems like everyone is talking about thin provisioning. It's no miracle cure, but the technology can do wonders.

It appears that thin provisioning is finally a mainstream technology. With Hitachi Data Systems recently announcing its Universal Storage Platform (USP) V with thin provisioning (called Dynamic Provisioning) and EMC making its Virtual Provisioning announcement, it's only a matter of time before all of the other storage vendors will be touting thin provisioning as a new feature in their product lines.

But thin provisioning isn't new. Companies such as 3PAR and other smaller players have been selling it as a core feature of their product lines for a while. With the buzz around virtualization, this technology has suddenly become interesting to more players because it offers a new approach to how storage is provisioned.

Is thin provisioning truly a miracle technology? Not really. It's not a tool that can magically provide you with more capacity than you purchased. However, it does let you allocate only what's accessed while allowing the host to think it has access to everything it sees. For example, a 300GB logical unit is provisioned to a host. After creating a file system on it, only 100GB is used. At that point, the array intelligently figures out that the remaining 200GB isn't being used and keeps it in reserve. Yet the host happily continues

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to think it has access to the remaining 200GB.

Several vendors have deployed this technology in the form of a snapshot or copy-on-write feature for point-in-time copies. This allows customers to save big on storage purchases made for replica copies. The underlying premise is that change rates are never more than 20% to 30%. If you apply this concept to your primary storage, this suddenly becomes an interesting way to overprovision. But what happens if a host (or a set of hosts) suddenly needs more space? Again, there's a solution. If you pool all of the resources into a single bucket (often known as the resource pool), then any server or set of servers can borrow against its allocated resources on an as-needed basis.

The caveat is that not all of the servers sharing the pool can borrow space at the same time. Think of it like your local savings bank. The bank pools funds into a single bucket and invests them with the assumption that not everyone will withdraw all of their money at the same time.

So does this mean you can purchase less storage than you need? Not really. But it lets you manage your resources more effectively, rather than cater to storage requirements in an ad-hoc manner. You now have better control over allocation, and you can perform a trend analysis of how storage is consumed as a function of the global resource pool.

This was first published in April 2008

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