A device is just a random-access block device.

• vdevs are made of individual devices, and the zpool is made of vdevs.
• Anything with a descriptor in /dev that allows random access will work.

vdevs can be built from:

• Disks - The most common block devices.
• Entire hardware RAID arrays can used as individual devices.
• Simple raw files.
  • Test pools made of sparse files are an incredibly convenient way to practice zpool commands, and see how much space is available on a pool or vdev of a given topology.