This section does not discuss all the terminology that is used for disks, such as track, cylinder, sector, and so on. For explanations of the meaning of these terms, refer to numerous information sources about hard disks, such as http://en.wikipedia.org/wiki/Hard_disk_drive, or the disk manufacturer's documentation.
The following concepts are useful to understand disk management in Oracle Solaris.
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.
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. On Fujitsu M10 servers, the firmware must be at least version XCP 2230 or later.
x86 systems
The Oracle Solaris ZFS file system supports file systems that are greater than 1 TB in size.
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.
Files on a disk are contained in file systems. Each file system on a disk is assigned to a slice comprising of a group of sectors. Slices are sometimes referred to as partitions. Certain interfaces, such as the format utility, refer to slices as partitions.
Each disk slice appears as a separate disk drive.
When setting up slices, remember these rules:
Each disk slice holds only one file system.
No file system can span multiple slices.
For information about file systems, see Managing File Systems in Oracle Solaris 11.3.
Third-party database applications typically create raw data slices. These applications must not use block 0 or slice 2 for raw slices. Block 0 stores the disk label while slice 2 represents the entire disk with a VTOC label. Creating raw slices on these two locations overwrites the disk label and renders data on the disk inaccessible.
When you use the format utility to change the size of one or more disk slices, you designate a temporary slice that will expand and shrink to accommodate the resizing operations.
This temporary slice donates, or “frees,” space when you expand a slice, and receives, or “hogs,” the discarded space when you shrink a slice. For this reason, the donor slice is sometimes called the free hog.
The free hog slice exists only during installation or when you run the format utility. There is no permanent free hog slice during day-to-day operations.
For information on using the free hog slice, see How to Replace a ZFS Root Pool (VTOC) or How to Replace a ZFS Root Pool (EFI (GPT)).