My Mac Says Drobo Has More Capacity Than It Actually Does

Drobo, Drobo S and Drobo FS:

When you look at the properties for your Drobo storage device using any of your Mac tools, such as Finder or Get Info, you will find that your Mac might report that your Drobo product has more capacity than it actually does. Mac OS X will report the volume size you choose in Drobo Dashboard during the initial setup and NOT the actual total physical capacity of the drives in your Drobo device. This volume size is independent of how much actual physical storage you have in your device. This feature (called thin provisioning) allows Drobo devices to easily expand capacity in the future, without forcing complex management and configuration. Mac OS X will however accurately report actual capacity used on your Drobo storage device.

Drobo storage devices let you add capacity quickly and easily, whenever you need it, by simply adding an additional drive or replacing a lower capacity drive with a higher capacity drive. When you add enough actual hard drive capacity for your Drobo device to exceed the set volume size, it will simply create a new volume on your Mac resulting in an additional "virtual" drive. Drobo Dashboard will walk you through the process when this occurs. The new volume will show up on your Mac as a separate volume and the size will again show as the size set up in Drobo Dashboard.

For example, say during the initial setup, you chose 2TB as your volume size, even though you only had 1.5TB of actual physical storage in your Drobo device. When you add enough drive capacity to exceed 2TB (for example, inserting two more 1TB drives in Drobo), Drobo will create an additional volume. In this example, Mac OS X will show two separate 2TB volumes. If you want to avoid this creation of multiple volumes, you should select a larger volume size during the initial format process when first setting up your Drobo storage device. See Formatting Drives Using Drobo Dashboard. Depending on your version of the operating system, you can create volumes up to 16TB.

You can determine actual disk space usage by opening Drobo Dashboard or in Mac OS X. For a quick assessment, the blue capacity lights on the front of your Drobo provide an approximation in 10 percent increments. Additionally, Drobo storage devices will always warn you if you are starting to run low on available space.

DroboPro and DroboElite:

Though the same principles as above apply to the way Windows will display volume size information, the way new volumes are created is different. In DroboPro and DroboElite, you will be prompted to create a new volume using the Volume Management feature in Drobo Dashboard.