1.4.3 Compact or USB Flash
The FreeNAS® operating system is a running image. This means that it should not be installed onto a hard drive, but rather to a USB or compact flash device that is at least 2 GB in size. If you don't have compact flash, you can instead use a USB thumb drive that is dedicated to the running image and which stays inserted in the USB slot. While technically you can install FreeNAS® onto a hard drive, this is discouraged as you will lose the storage capacity of the drive. In other words, the operating system will take over the drive and will not allow you to store data on it, regardless of the size of the drive.
The FreeNAS® installation will partition the operating system drive into two ~1 GB partitions. One partition holds the current operating system and the other partition is used when you upgrade. This allows you to safely upgrade to a new image or to revert to an older image should you encounter problems.