Chapter 31 Managing Disks (Overview)

This chapter provides overview information about Solaris disk slices and introduces the format utility.

This is a list of overview information in this chapter.

• What's New in Disk Management?

• Where to Find Disk Management Tasks

• Overview of Disk Management

• Disk Terminology

• About Disk Slices

• The format Utility

• About Disk Labels

• Dividing a Disk Into Slices

For instructions on how to add a disk to your system, see Chapter 33, SPARC: Adding a Disk (Tasks) or Chapter 34, x86: Adding a Disk (Tasks).

What's New in Disk Management?

This section describes new disk management features in the Solaris 9 release.

Solaris Volume Manager and Soft Partitioning

The previously unbundled Solstice DiskSuite^TM product is now part of the Solaris 9 release and is called Solaris Volume Manager. Solaris Volume Manager's new partitioning feature, soft partitioning, enables more than eight partitions per disk.

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

Where to Find Disk Management Tasks

Use these references to find step-by-step instructions for managing disks.

Overview of Disk Management

The management of disks in the Solaris environment usually involves setting up the system and running the Solaris installation program to create the appropriate disk slices and file systems and to install the operating system. Occasionally, you might need to use the format utility to add a new disk drive or replace a defective one.

The Solaris operating environment runs on two types of hardware, or platforms—SPARC and IA. The Solaris operating environment runs on both 64–bit and 32–bit address spaces. The information in this document pertains to both platforms and address spaces unless called out in a special chapter, section, note, bullet, figure, table, example, or code example.

Disk Terminology

Before you can effectively use the information in this section, you should be familiar with basic disk architecture. In particular, you should be familiar with the following terms:

For additional information, see the product information from your disk's manufacturer.

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).

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:

• Each disk slice holds only one file system.

• No file system can span multiple slices.

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

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.

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.

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:

• Block 0 where the disk label is stored

• Slice 2, which represents the entire disk

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.

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:

• Servers

• Standalone systems

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

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

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

The format Utility

Read the following overview of the format utility and its uses before proceeding to the “how-to” or reference sections.

The format utility is a system administration tool that is used to prepare hard disk drives for use on your Solaris system.

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

The format utility options are fully described in Chapter 35, The format Utility (Reference).

When to Use the format Utility

Disk drives are partitioned and labeled by the Solaris installation program when you install the Solaris release. You can use the format utility to do the following:

• Display slice information

• Divide a disk into slices

• Add a disk drive to an existing system

• Format a disk drive

• Label a disk

• Repair a disk drive

• Analyze a disk for errors

The main reason a system administrator uses the format utility is to divide a disk into disk slices. These steps are covered in Chapter 33, SPARC: Adding a Disk (Tasks) and Chapter 34, x86: Adding a Disk (Tasks).

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

Guidelines for Using the format Utility

Formatting a Disk

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

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

When you format a disk, you accomplishes two steps:

• The disk media is prepared for use

• A list of disk defects based on a surface analysis is compiled

Formatting a disk is a destructive process because 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 the cause of recurring problems, you can use the format utility to do a surface analysis. However, be careful to use only the commands that do not destroy data. For details, see How to Format a Disk.

A small percentage of total disk space that is 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 a disk might take anywhere from a few minutes to several hours, depending on the type and size of the disk.

About Disk Labels

A special area of every disk is set aside for storing information about the disk's controller, geometry, and slices. That information is called the disk's label. Another term that is used to described the disk label is the VTOC (Volume Table of Contents). To label a disk means to write slice information onto the disk. You usually label a disk after you change its slices.

If you fail to label a disk after you create slices, the slices will be unavailable because the operating system has no way of “knowing” about the slices.

Partition Table

An important part of the disk label is the partition table, which identifies a disk's slices, the slice boundaries (in cylinders), and the total size of the slices. You can display a disk's partition table by using the format utility. The following table describes partition table terminology.

Partition flags and tags are assigned by convention and require no maintenance.

For more information on displaying the partition table, see How to Display Disk Slice Information or How to Examine a Disk Label.

Displaying Partition Table Information

The following is an example of a partition table from a 1.05-Gbyte disk by using the format utility:

Total disk cylinders available: 2036 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders        Size            Blocks
  0       root    wm       0 -  300      148.15MB    (301/0/0)   303408
  1       swap    wu     301 -  524      110.25MB    (224/0/0)   225792
  2     backup    wm       0 - 2035     1002.09MB    (2036/0/0) 2052288
  3 unassigned    wm       0               0         (0/0/0)          0
  4 unassigned    wm       0               0         (0/0/0)          0
  5 unassigned    wm       0               0         (0/0/0)          0
  6        usr    wm     525 - 2035      743.70MB    (1511/0/0) 1523088
  7 unassigned    wm       0               0         (0/0/0)          0

The partition table displayed by the format utility contains the following information:

The following is an example of a disk label displayed by using the prtvtoc command.

# prtvtoc /dev/rdsk/c0t1d0s0
* /dev/rdsk/c0t1d0s0 partition map
*
* Dimensions:
*     512 bytes/sector
*      72 sectors/track
*      14 tracks/cylinder
*    1008 sectors/cylinder
*    2038 cylinders
*    2036 accessible cylinders
*
* Flags:
*   1: unmountable
*  10: read-only
*
*                          First     Sector    Last
* Partition  Tag  Flags    Sector     Count    Sector  Mount Directory
       0      2    00          0    303408    303407   /
       1      3    01     303408    225792    529199
       2      5    00          0   2052288   2052287
       6      4    00     529200   1523088   2052287   /usr

The prtvtoc command provides the following information:

Dividing a Disk Into Slices

The format utility is most often used by system administrators to divide a disk into slices. The steps are as follows:

• Determining which slices are needed

• Determining the size of each slice

• Using the format utility to divide the disk into slices

• Labeling the disk with new slice information

• Creating the file system for each slice

The easiest way to divide a disk into slices is to use the modify command from the partition menu of the format utility. The modify command allows you to create slices by specifying the size of each slice in Mbytes without having to keep track of the starting cylinder boundaries. The modify command also keeps tracks of any disk space that remains in the “free hog” slice.

Using the Free Hog Slice

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 SPARC: How to Create Disk Slices and Label a Disk or IA: How to Create Disk Slices and Label a Disk.