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An introduction to dynamic storage provisioning for Windows

One of the easiest ways for Windows shops to reduce IT spending is through dynamic storage provisioning.

While you may be unfamiliar with the term, the concept of dynamic storage provisioning

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has been around for years. With this method, disk space is treated as a pool of resources that can be distributed on an as needed basis. A variety of products use dynamic storage provisioning, including Microsoft System Center Data Protection Manager 2007, which allocates disk space to each protected resource from a centralized storage pool.

How dynamic storage provisioning reduces costs

When an administrator is asked to deploy a new file or application server, they don't immediately purchase the necessary hardware. Instead, they do some capacity planning to figure out what they need.

As I'm sure you know, capacity planning is something of an art form. You want your new server to have all the resources it needs now and for future growth, but you don't want to break the bank.

Since disk space is usually cheap, Windows administrators can be a bit overzealous when estimating a server's storage requirements. Still, this zeal isn't completely unwarranted.

For example, an administrator may have to deploy a new application server. Through capacity planning they determine that the server would need about 500 GB of disk space, but in all likelihood, he or she will put a couple of terabytes of storage in the server. There are three main reasons why over-provisioning a server's storage resource like this is justified:

  1. Required storage estimates are sometimes wrong. It is important to have enough extra disk space to make up for inaccurate estimates and to accommodate future growth.
  2. Nobody wants to explain to their boss that they underestimated the system requirements for the server and need to order additional hardware.
  3. While adding extra disk space to a server later on probably won't break the bank, extending the existing storage volumes to make use of the new space almost always requires some downtime. Since downtime is often unacceptable, it may be preferred to initially provide the server with more disk space than should ever be used.

Although there are some good reasons for over-provisioning server storage, remember that storage comes at a price. For example, a 400 GB Fibre Channel drive with a transfer rate of 4 GB per second currently costs about $550. That is about 82 cents per gigabyte. At that rate, it is easy to see how much money can be wasted by provisioning servers with more storage space than necessary.

This is where dynamic storage provisioning comes into play. Many of the dynamic storage provisioning products on the market use a technique called thin provisioning, which allows you to provision a server with specific storage resources even though those resources are not used until they are needed.

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To see how this works, consider the earlier example where a network administrator provisioned a server with 2 TB even though it was estimated that the server would only consume about 500 GB of storage. Also, assume that initially the server was consuming 200 GB of storage space.

With thin provisioning, the administrator can still provision the server with the same 2 TB of storage space. The difference, however, is that this 2 TB comes from a central storage pool and isn't used all at once. In this case, only 200 GB of the available 2 TB would initially be used. A storage price of 82 cents per gigabyte would result in an immediate savings of $1515.36 (2048 GB - 200 GB *$0 .82).

You are probably thinking these savings are all theoretical because the storage space still has to be purchased before it can be allocated to the server -- but that's not the case.

Certain thin provisioning products let you allocate more space than what is actually available, assuming that more physical storage space will be added to the storage pool if the space needed exceeds what is available.

Thin provisioning has been compared to the way that airlines overbook flights. The airlines routinely overbook just about every flight because they know that some people won't show up. Therefore, they usually get away with selling tickets to more passengers than the planes can hold. Thin provisioning works the same way. If you are pretty sure your server is never going to use more than 500 GB of storage, you can safely allocate 2 TB to that server, because the extra 1.5 TB will probably never be used. Even if the 500 GB threshold is exceeded, it probably won't be exceeded by much.

Allocating more disk space than what is needed ensures servers won't have to be taken offline to resize volumes. If the storage pool begins running low on disk space, the problem can be solved simply by adding more physical disk to the storage pool. This can often be done without disrupting file or application servers.

Overall, dynamic server provisioning has the potential to save money by reducing the amount of wasted disk space. It is also good for ensuring that servers do not have to be taken offline every time they begin to run low on storage space.

Brien M. Posey, MCSE, has received Microsoft's Most Valuable Professional Award four times for his work with Windows Server, IIS and Exchange Server. He has served as CIO for a nationwide chain of hospitals and healthcare facilities, and was once a network administrator for Fort Knox. You can visit his personal Web site at www.brienposey.com.


This was first published in January 2010

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