Space Reclamation: If Being Thin is Attractive, Then Thin Provisioning Makes for Really Sexy Storage

Sorry, this article isn’t about attractive people, but it is about saving attractive dinero in your data center.


In business school, I remember being presented with a learning exercise that went something like this: Let me offer you two finance options to purchase your product, assuming it is worth $100k in today’s dollars. Here are your choices:

  1. $100k cash money today, or
  2. $0.01 today, and for the next 4 weeks, I will double the previous day’s payment


Which option do you pick?


This transaction illustrates a classic example of the power of compound interest. If you need the money today, well, you take the money today. But, the second alternative is worth much more. WAY more, in fact. When you do the math, it is worth over $1 Million, or over 10 times the amount of option 1!


If you reverse the illustration, you essentially demonstrate the principle of depreciable assets. What you buy today will be much less valuable over time. And that is especially true for IT commodities like disk drives. Disk capacities continue to increase and prices continue to drop. The $/GB equation gets better over time. So, why purchase more capacity than you need today when you can buy the same capacity at a lower price when you need it later?


NetApp’s Thin Provisioning deployed with NetApp’s FlexVol technology allows you to allocate storage on demand as data is written to disk, instead of preallocating all of the capacity ahead of time. So, you only buy today according to your data storage requirements rather than commit to a storage purchase for some eventual future requirement. After all, why provision all of the capacity before you know you will ever use it? It is just wasted space.  You can put off storage purchases for empty space until you need to store data, and when disk capacity is cheaper. Not bad.


Figure 1 illustrates the advantages of thin provisioning compared with the traditional storage provisioning.

Figure 1 Traditional provisioning versus thin provisioning.


And the picture looks even nicer when you include space reclamation. Space reclamation complements thin provisioning to reduce inefficiency in your storage by identifying data blocks that aren’t needed by the applications that are still being consumed by the storage. In other words, if you have data stored on a LUN and it is consuming space, and then data is deleted, without space reclamation, the storage controller wouldn’t know that those blocks are free to add back to the available pool. A mechanism between the application and the storage is required to tell the storage that blocks freed up by the application can be reclaimed by the storage controller for use with other applications.

Figure 2 Typical host versus storage LUN space utilization: Delete File2.


NetApp delivers the value of space reclamation with our SnapDrive client software, which is an OS specific application that facilitates the creation of volumes and LUNs and helps orchestrate Snapshot operations with NetApp FAS and V-Series storage. It also helps to identify free blocks to be reclaimed by NetApp storage.


Additionally, NetApp works with OS and application vendors to enable this functionality without the requirement of an additional client application. Our latest effort is work done with Red Hat. We have released a new deployment guide entitled NetApp Thin-Provisioned LUNs on RHEL 6.2 Deployment Guide that outlines space reclamation best practices on Red Hat Linux. This new deployment guide complements other guides, such as the NetApp and VMware View Solution Guide and Maximize Storage Efficiency with NetApp Thin Provisioning and Symantec Thin Reclamation.


We have been discussing this topic for a while at NetApp. So, check out some other articles on this topic:

  1. NetApp and Symantec Enhance Thin Provisioning for SAN Environments
  2. Thin Provisioning Video
  3. SnapDrive 6.3:  Support for VMFS and NFS
  4. Punching Hole


Go on. And get thin.