Before the days of electronic check processing, people would sometimes float checks. The trick to floating a check was ensuring that you had enough money in the bank to cover the check by the time it cleared the bank. Thin provisioning works the same way. You are essentially floating a storage check and need to have the storage physically in place by the time it’s actually needed. This means you can allocate as much space as you want in the volume, but only add disks when the volume or aggregate is almost full. This is why thin provisioning is sometimes referred to as “storage on demand” or “just-in-time storage”.
The trick is that you have to always monitor your storage system to ensure that you know when it’s time to add additional disks. You can monitor this manually, using reports from something like Operations Manager, or using some scripting some type of alert yourself. The problem with thin provisioning is that administrators have to monitor the storage system carefully, or over time, the volume will fill up and the volume or LUN will go offline.
Planning and monitoring are very important when managing thin provisioning and a short procurement cycle is also critical. If it will take a month to purchase new drives and you suddenly run out of space, your only option for getting the LUN back online will be delete snapshots or delete data to get the LUN back online. Thin provisioning can be used with both volumes and LUNs. In order to do thin provisioning, you must be using flexible volumes. For more information on flexible volumes and aggregates, please see last week’s post.
In order to setup thin provisioning, you simply create the volume with the space guarantee set to none. This means that space for the volume is not guaranteed within the aggregate, the volume will simply grow as space is used until the volume size specified is reached.
From the technical perspective, configuring thin provisioning is fairly straightforward. In FilerView, you set the guarantee setting to none while you are creating the volume. If you prefer to configure thin provisioning from the command line, you will need to use the vol options command to change the guarantee setting to none. You must do this for every volume that you wish to thin provision.
Thin provisioning can produce a tremendous savings because your volumes do not have to be space guaranteed when they are created. The catch for you as the administrator is that you will have to ensure that you have adequate disks available when you need them. Next week, we’ll continue our discussion on NetApp storage efficiencies with FlexClones.