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System Administration Guide: Basic Administration

About Disk Slices

Files stored on a disk are contained in file systems. Each file system on a disk is assigned to a slice, which is a group of sectors set aside for use by that file system. Each disk slice appears to the operating system (and to the system administrator) as though it were a separate disk drive.

For information about file systems, see Chapter 37, Managing File Systems (Overview).

Note –

Slices are sometimes referred to as partitions. This book uses slice but certain interfaces, such as the format utility, refer to slices as partitions.

When setting up slices, remember these rules:

Slices are set up slightly differently on SPARC and IA platforms. The following table summarizes the differences.

Table 31–1 Slice Differences on Platforms

SPARC Platform 

IA Platform 

Whole disk is devoted to Solaris environment 

Disk is divided into fdisk partitions, one fdisk partition per operating environment

Disk is divided into 8 slices, numbered 0–7 

The Solaris fdisk partition is divided into 10 slices, numbered 0–9

SPARC: Disk Slices

On SPARC based systems, Solaris defines eight disk slices and assigns to each a conventional use. These slices are numbered 0 through 7. The following table summarizes the contents of the eight Solaris slices on a SPARC based system.

Table 31–2 SPARC: Customary Disk Slices

Slice 

File System 

Usually Found on Client or Server Systems? 

Purpose 

0 

root (/)

Both 

Holds files and directories that make up the operating system. 

1 

swap 

Both 

Provides virtual memory, or swap space. Swap space is used when running programs are too large to fit in a computer's memory. The Solaris operating environment then “swaps” programs from memory to the disk and back, as needed.

2 

— 

Both 

Refers to the entire disk, by convention. This slice is defined automatically by the format utility and the Solaris installation programs. The size of this slice should not be changed.

3 

/export

Server only 

Holds alternative versions of the operating system. These alternative versions are required by client systems whose architectures differ from that of the server. Clients with the same architecture type as the server obtain executables from the /usr file system, usually slice 6.

4 

 

 

Optional slice to be defined based on your site's needs. 

5 

 

 

Optional slice to be defined based on your site's needs. 

Can be used to hold application software added to a system. If a slice is not allocated for the /opt file system during installation, the /opt directory is put in slice 0.

6 

/usr

Both 

Holds operating system commands (also known as executables). This slice also holds documentation, system programs (init and syslogd, for example) and library routines.

7 

/home or

/export/home

Both 

Holds files that are created by users. 

x86: Disk Slices

On IA based systems, disks are divided into fdisk partitions. An fdisk partition is a section of the disk that reserved for a particular operating environment, such as the Solaris release.

The Solaris release places ten slices, numbered 0–9, on a Solaris fdisk partition as shown in the following table.

Table 31–3 x86: Customary Disk Slices

Slice 

File System 

Usually Found on Client or Server Systems? 

Purpose 

0 

root (/) 

Both 

Holds the files and directories that make up the operating system. 

1 

swap 

Both 

Provides virtual memory, or swap space. Swap space is used when running programs are too large to fit in a computer's memory. The Solaris operating environment then “swaps” programs from memory to the disk and back, as needed.

2 

— 

Both 

Refers to the entire disk, by convention. This slice is defined automatically by the format utility and the Solaris installation programs. The size of this slice should not be changed.

3 

/export

Server only 

Holds alternative versions of the operating system. These alternative versions are required by client systems whose architectures differ from that of the server.  

4 

 

 

Optional slice to be defined based on your site's needs. 

5 

 

Both 

Optional slice to be defined based on your site's needs. 

Can be used to hold application software added to a system. If a slice is not allocated for the /opt file system during installation, the /opt directory is put in slice 0.

6 

/usr

Both 

Holds operating system commands (also known as executables). This slice also holds documentation, system programs (init and syslogd, for example) and library routines.

7 

/home or /export/home

Both 

Holds files that are created by users. 

8 

— 

Both 

Contains information necessary for to boot the Solaris environment from the hard disk. The slice resides at the beginning of the Solaris fdisk partition (although the slice number itself does not indicate this fact), and is known as the boot slice.

9 

— 

Both 

Provides an area that is reserved for alternate disk blocks. Slice 9 is known as the alternate sector slice. 

Using Raw Data Slices

The SunOS operating system stores the disk label in block 0 of each disk. So, third-party database applications that create raw data slices must not start at block 0, or the disk label will be overwritten and the data on the disk will be inaccessible.

Do not use the following areas of the disk for raw data slices, which are sometimes created by third-party database applications:

Slice Arrangements on Multiple Disks

Although a single large disk can hold all slices and their corresponding file systems, two or more disks are often used to hold a system's slices and file systems.

Note –

A slice cannot be split between two or more disks. However, multiple swap slices on separate disks are allowed.

For instance, a single disk might hold the root (/) file system, a swap area, and the /usr file system, while another disk holds the /export/home file system and other file systems that contain user data.

In a multiple disk arrangement, the disk that contains the operating system software and swap space (that is, the disk that holds the root (/) and /usr file systems and the slice for swap space) is called the system disk. Other disks are called secondary disks or non-system disks.

When you arrange a system's file systems on multiple disks, you can modify file systems and slices on the secondary disks without having to shut down the system or reload operating system software.

When you have more than one disk, you also increase input-output (I/O) volume. By distributing disk load across multiple disks, you can avoid I/O bottlenecks.

Determining Which Slices to Use

When you set up a disk's file systems, you choose not only the size of each slice, but also which slices to use. Your decisions about these matters depend on the configuration of the system to which the disk is attached and the software you want to install on the disk.

System configurations that need disk space are as follows:

Each system configuration requires the use of different slices. The following table lists these requirements.

Table 31–4 System Configurations and Slice Requirements

Slice 

Servers 

Standalone Systems 

0 

root 

root 

1 

swap 

swap 

2 

— 

— 

3 

/export

— 

6 

/usr

/usr

7 

/export/home

/home

For more information about system configurations, see Overview of System Types.

Note –

The Solaris installation program provides slice size recommendations based on the software you select for installation.