System Administration Guide, Volume 1

The format Utility

Read the following information if you want to see a conceptual view of the format utility and it uses before proceeding to the "how-to" or reference sections.


The format utility is a system administration tool used to prepare hard disk drives for use on your Solaris system. The format utility cannot be used on diskette drives, CD-ROM drives, or tape drives.

Features and Benefits

The table below shows the features and associated benefits that the format utility provides.

Table 28-5 Features and Benefits of the format Utility



Searches your system for all attached disk drives 


  • Target location

  • Disk geometry

  • Whether the disk is formatted

  • If the disk has mounted partitions

Retrieves disk labels 

Used in repair operations 

Repairs defective sectors 

Allows administrators to repair disk drives with recoverable errors instead of sending the drive back to the manufacturer 

Formats and analyzes a disk 

Creates sectors on the disk and verifies each sector 

Partitions a disk 

Divides a disk so individual file systems can be created on separate slices 

Labels a disk 

Writes disk name and configuration information to the disk for future retrieval (usually for repair operations) 

All of the options of the format utility are fully described in Chapter 32, The format Utility (Reference).

When to Use the format Utility

Disk drives are partitioned and labeled by the Solaris installation program as part of installing the Solaris release. You might need to use the format utility when:

The main reason a system administrator uses the format utility is to divide a disk into disk slices. These steps are covered in Chapter 30, SPARC: Adding a Disk (Tasks) and Chapter 31, IA: Adding a Disk (Tasks).

See the section below for guidelines on using the format utility.

Guidelines for Using the format Utility

Table 28-6 The format Utility Guidelines

Use format To ...

Considerations ... 

Where to Go ... 

Format a disk 

  • Any existing data will be destroyed when a disk is reformatted.

  • The need for formatting a disk drive has dropped as more and more manufacturers ship their disk drives formatted and partitioned. You might not need to use the format utility when adding a disk drive to an existing system.

  • If a disk has been relocated and is displaying a lot of disk errors, you can attempt to reformat it, which will automatically remap any bad sectors.

"How to Format a Disk"

Replace a system disk 

  • Data from the damaged system disk must be restored from a backup medium; otherwise the system will have to be reinstalled by using the installation program.

Chapter 30, SPARC: Adding a Disk (Tasks) or Chapter 31, IA: Adding a Disk (Tasks) or if the system must be reinstalled, Solaris 8 Advanced Installation Guide

Divide a disk into slices 

  • Any existing data will be destroyed when a disk with existing slices is repartitioned and relabeled.

  • Existing data must be copied to backup media before the disk is repartitioned and restored after the disk is relabeled.

Chapter 30, SPARC: Adding a Disk (Tasks) or Chapter 31, IA: Adding a Disk (Tasks)

Add a secondary disk to an existing system 

  • Any existing data must be restored from backup media if the secondary disk is reformatted or repartitioned.

Chapter 30, SPARC: Adding a Disk (Tasks) or Chapter 31, IA: Adding a Disk (Tasks)

Repair a disk drive 

  • Some customer sites prefer to replace rather than repair defective drives. If your site has a repair contract with the disk drive manufacturer, you might not need to use the format utility to repair disk drives.

  • Repairing a disk drive usually means that a bad sector is added to a defect list. New controllers remap bad sectors automatically with no system interruption.

  • If the system has an older controller, you might need to remap a bad sector and restore any lost data.

Chapter 32, The format Utility (Reference)

Formatting a Disk

In most cases, disks are formatted by the manufacturer or reseller and do not need to be reformatted when you install the drive. To determine whether or not a disk is formatted, use the format utility. See "How to Determine if a Disk is Formatted" for more information.

If you determine that a disk is not formatted, use the format utility to format the disk.

Formatting a disk accomplishes two steps:

Caution - Caution -

Formatting is a destructive process--it overwrites data on the disk. For this reason, disks are usually formatted only by the manufacturer or reseller. If you think disk defects are causing recurring problems, you can use the format utility to do a surface analysis, but be careful to use only the commands that do not destroy data. See "How to Format a Disk" for details.

A small percentage of total disk space available for data is used to store defect and formatting information. This percentage varies according to disk geometry, and decreases as the disk ages and develops more defects.

Formatting might take anywhere from a few minutes to several hours, depending on the type and size of the disk.