A special area of every disk is set aside for storing information about the disk's controller, geometry, and slices. This information is called the disk's label. Another term that is used to described the disk label is the VTOC (Volume Table of Contents) on a disk with a VTOC label. To label a disk means to write slice information onto the disk. You usually label a disk after you change its slices.
The Solaris release supports the following two disk labels:
SMI – The traditional VTOC label for disks that are less than 2 TB in size.
EFI – Provides support for disks that are larger than 2 TB on systems that run a 64-bit Solaris kernel. The Extensible Firmware Interface GUID Partition Table (EFI GPT) disk label is also available for disks less than 2 TB that are connected to a system that runs a 32-bit Solaris kernel.
If you fail to label a disk after you create slices, the slices will be unavailable because the OS has no way of “knowing” about the slices.