Allocation of storage the number one challenge facing most data centers today. In larger environments, it can take days or weeks to provision out storage. This leads to over allocation of the storage upfront (the overbuy phenomenon mentioned above), meaning that an Oracle DBA will ask for 500GB of storage space for their environment when, to start with, they only need a few hundred megabytes. This eliminates one of the key advantages a Storage Area Network (SAN) has over direct attached storage. One of the major reasons to move to a SAN was to release captive storage so it could be better balanced across the enterprise. By being forced to allocate storage that will not be used you are in effect recreating the same problem. In a typical SAN environment, as much as 50% of the storage is allocated but not used. 

The answer to this problem is thin provisioning. Thin provisioning allows you to allocate storage before it is actually used. With thin provisioning, you only consume the physical  storage as the application writes to it. Therefore, you are leveraging the probability that the actual consumers of the storage will never use all the capacity they thought they would or they will consume that storage so slowly that you will be able to back fill storage capacity prior to them needing it. This is a tremendous cost saver.

Customers I speak with that have a product that provides thin provisioning love it, are seeing significant cost savings and experiencing limited to no technical issues. Customers are now demanding the capability and as a result, many suppliers are racing to provide this capability to the market. Experience matters here and like other technologies, systems that have had thin provisioning built in from inception tend to execute better. Look for suppliers that have a deep customer list of people truly using thin provisioning. When you add a feature like thin provisioning to a SAN array, suppliers end up learning a lot. Make sure they have already completed their education prior to you being a customer.

How does thin provisioning work? For example, let's say you have an Oracle DBA request a 500GB volume for a new Oracle environment. Without thin provisioning, you would have to assign and provision that 500GB, making that capacity unavailable to any other server on the SAN. You could also ignore their request for 500GB of storage, provision them less and then deal with the application and possible system downtime later, but that is problematic. With thin provisioning, you can assign a 500GB or even 1TB size volume to the Oracle server, but you do not have to actually consume that physical storage. The only storage space that is allocated is the storage space used as the database is created and written to. Initially this may mean only a few hundred megabytes. Allowing the other 499GB’s to be available to other servers. As the capacity needs of the application grow and new data is written to the volume, it expands without any effort from you or downtime to the server or application using that volume. 

This provides a significant cost reduction in three areas. First, you use less upfront storage. Second, the longer you can delay the purchase of storage the less expensive it will be. Lastly, you save space in a DR site because the only data that needs to be replicated and stored is this actual data, not all the white space associated with the volume. 

Thin provisioning is a significant time saver as well. You don’t have to spend as much time carefully planning how much storage each application will use, since these volumes will now allocate space on the fly without storage administrator intervention. This allows the storage administrator to spend less time allocating storage and more time making sure that storage is well protected. The original promise of SANs was that they would better eliminate captive storage on single servers and allocate that storage across multiple servers. What ended up happening is that the storage became captive in a central location. Thin provisioning delivers on the promise by not physically pre-allocating storage until it is needed. 

How do you make sure you don’t really run out of disk space? Most of the system vendors that supply this provisioning provide excellent reporting to give you advanced warning if you are running out of physical disk space. I recommend having a pre-approved purchase order, if possible, that will allow you to quickly purchase additional storage. Some of the Storage suppliers can take automated actions to reclaim space if you do begin to run out of actual storage space; for example, deleting old snapshots.

In addition, as mentioned earlier, make sure you work with a supplier that has had thin provisioning built into their storage array from the beginning. Suppliers are racing to add this “check-mark” to their feature set, but in many cases, they are not delivering on the complete promise. If you have to stop an application, stop a server or do any major manual intervention then it is not “real” thin provisioning and will not deliver near the same benefits.

In either workaround scenario, you are exposed to some sort of downtime and you can only expand a volume so many times.

Thin provisioning is one of the most significant advances in storage and delivers on one of the real promises of SAN's; freeing captive storage to increase storage efficiencies, greatly reducing storage costs, power consumption and maintenance contract costs. Along with hard costs, it can be one of the single biggest time savers to burdened IT staffs and data consumers.