EFI (GPT) Disk Label

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A disk label stores information about the disk's controller, geometry, and slices. A disk label is also called the VTOC (Volume Table of Contents) label.

Labeling a disk means writing slice information onto the disk. You usually label a disk after you change its slices or partitions. By means of the label, the OS is informed about the slices. If you fail to label a disk after you create slices, the slices will be unavailable.

Oracle Solaris supports the following disk labels:

SMI – Traditional VTOC label for disks that are less than 2 TB in size.
EFI – Label for disks that are larger than 2 TB. However, the Extensible Firmware Interface GUID Partition Table (EFI GPT) disk label is also available for disks less than 2 TB.

Note - You can continue to use the VTOC label on any size disk, but the addressable space by the VTOC is limited to 2 TB.

In Oracle Solaris, an EFI (GPT) labeled disk is installed by default on the following systems:

SPARC systems with GPT enabled firmware

On SPARC T4 servers, the Sun System Firmware must be at least version 8.4.0. On SPARC T5 and SPARC M5 servers, the firmware must be at least version 9.1.0.
x86 systems

The Oracle Solaris ZFS file system supports file systems that are greater than 1 TB in size.

Note - The legacy Solaris Volume Manager software can also be used to manage disks that are greater than 1 TB, but a root disk that is managed by Solaris Volume Manager cannot be used for booting the Oracle Solaris 11 release.

The following additional features differentiate the EFI disk label from the VTOC disk label:

Provides usable slices 0-6, where partition 2 is just another slice.
Prohibits overlap of partitions or slices with a primary or backup label, or with other partitions. The size of the EFI label is usually 34 sectors, so partitions usually start at sector 34. Thus, no partition can start at sector zero (0). The entire disk is represented by cxtydz.
Does not use the notion of geometry. Partitions in EFI (GPT) labeled disks are defined based on logical blocks. Thus the EFI disk label provides information about disk or partition sizes in sectors and blocks, but not in cylinders and heads.
Stores information in the last two cylinders of a disk or partition instead of in an alternate cylinder area.
Supports reassigning partition tags after partition sizes are changed, except the unassigned partition tag which is assigned only to partitions with sizes equal to zero.

Before deciding to use EFI disks, consider that layered software products that are intended for systems with VTOC-labeled disks might be incapable of accessing a disk with an EFI disk label.