System Administration Guide: Basic Administration

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.