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System Administration Guide: Devices and File Systems

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 15, 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 x86 platforms. The following table summarizes the differences.

Table 10–1 Slice Differences on Platforms

SPARC Platform 

x86 Platform 

Whole disk is devoted to Solaris environment. 

Disk is divided into fdisk partitions, one fdisk partition per operating system.

VTOC – Disk is divided into 8 slices, numbered 0–7.

EFI – Disk is divided into 7 slices, numbered 0–6.

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

Solaris Volume Manager, previously Solstice DiskSuiteTM, has a partitioning feature, soft partitioning, that enables more than eight partitions per disk.

For general information about Solaris Volume Manager, see Chapter 2, Storage Management Concepts, in Solaris Volume Manager Administration Guide. For information on soft partitioning, see Chapter 12, Soft Partitions (Overview), in Solaris Volume Manager Administration Guide.

SPARC: Disk Slices

The following table describes the slices on a SPARC based system.

Table 10–2 SPARC: Customary Disk Slices

Slice 

File System 

Usually Found on Client or Server Systems? 

Comments 

0 

root (/)

Both 

Holds files and directories that make up the operating system. 

EFI – You cannot boot from a disk with an EFI label.

1 

swap 

Both 

Provides virtual memory, or swap space.

2 

— 

Both 

VTOC – Refers to the entire disk, by convention. The size of this slice should not be changed.

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

3 

/export

Both 

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

Can be used on a server to hold alternative versions of operating systems that are required by client systems. 

4 

 

Both 

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 

VTOC – Holds files that are created by users.

EFI – Not applicable.

8 

N/A 

N/A 

VTOC – Not applicable.

EFI – A reserved slice created by default. This area is similar to the VTOC's alternate cylinders. Do not modify nor delete this slice.

x86: Disk Slices

On x86 based systems, disks are divided into fdisk partitions. An fdisk partition is a section of the disk that reserved for a particular operating system, 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 10–3 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.

2 

— 

Both 

Refers to the entire disk, by convention. The size of this slice should not be changed. 

3 

/export

Both 

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

Can be used on a server to hold alternative versions of operating systems that are required by client systems. 

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 can use slices in a different way. The following table lists some examples.

Table 10–4 System Configurations and Slices

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 in System Administration Guide: Basic Administration.

Note –

The Solaris installation program provides default slice sizes based on the software you select for installation.