System Administration Guide, Volume 1

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 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 changing its slices.

If you fail to label a disk after creating 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 total size of the slices. A disk's partition table can be displayed using the format utility. The table below describes partition table terminology.

Table 28-7 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 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.

See "How to Display Disk Slice Information" or "How to Examine a Disk Label" for more information on displaying the partition table.

Examples--Partition Tables

The following partition table example is displayed from a 1.05-Gbyte disk 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 contains the following information:

Column Name	Description
`Part`	Partition (or slice number). See Table 28-7 for a description of this column.
`Tag`	Partition tag. See Table 28-7 for a description of this column.
`Flags`	Partition flag. See Table 28-7 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 example displays a disk label 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 disk label includes the following information:

Dimensions - This section describes the physical dimensions of the disk drive.

Flags - This section describes the flags listed in the partition table section. See Table 28-7 for a description of partition flags.

Partition (or Slice) Table - This section contains the following information:

Column Name	Description
`Partion`	Partition (or slice number). See Table 28-7 for a description of this column.
`Tag`	Partition tag. See Table 28-7 for a description of this column.
`Flags`	Partition flag. See Table 28-7 for a description of this column.
`First Sector`	The first sector of the slice.
`Sector Count`	The total number of sectors in the slice.
`Last Sector`	The last sector number in the slice.
`Mount Directory`	The last mount point directory for the file system.