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
Caution - 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.
Table 31-7 Partition Table Terminology
Partition Term | Value | Description |
|---|---|---|
Number | 0-7 | Partition (or slice number). Valid numbers are 0-7. |
Tag | 0=UNASSIGNED 1=BOOT 2=ROOT 3=SWAP 4=USR 5=BACKUP 7=VAR 8=HOME | A numeric value that usually describes the file system mounted on this partition. |
Flags | wm | The partition is writable and mountable. |
| wu rm | The partition is writable and unmountable. This is the default state of partitions that are dedicated for swap areas. (However, the mount command does not check the "not mountable" flag.) |
| rm | The partition is read only and mountable. |
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:
Column Name | Description |
|---|---|
Part | Partition (or slice number). See Table 31-7 for a description of this column. |
Tag | Partition tag. See Table 31-7 for a description of this column. |
Flags | Partition flag. See Table 31-7 for a description of this column. |
Cylinders | The starting and ending cylinder number for the slice. |
Size | The slice size in Mbytes. |
Blocks | The total number of cylinders and the total number of sectors per slice in the far right column. |
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:
Column Name | Description |
|---|---|
Dimensions | This section describes the physical dimensions of the disk drive. |
Flags | This section describes the flags listed in the partition table section. For a description of partition flags, see Table 31-7. |
Partition (or Slice) Table | This section contains the following information: |
Partition | Partition (or slice number). For a description of this column, see Table 31-7. |
Tag | Partition tag. For a description of this column, see Table 31-7. |
Flags | Partition flag. For a description of this column, see Table 31-7. |
| First Sector | The first sector of the slice. |
| Sector Count | The total number of sectors in the slice. |
Last Sector | The last sector of the slice. |
Mount Directory | The last mount point directory for the file system. |
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.