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) on a disk with a VTOC label. 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 32–7 Partition Table Terminology

Partition Term 

Value 

Description 

Number 

0-7

VTOC – Partitions or slices, numbered 0–7.

EFI – Partitions or slices, numbered 0–6.

Tag 

0=UNASSIGNED 1=BOOT 2=ROOT 3=SWAP 4=USR 5=BACKUP 7=VAR 8=HOME 11=RESERVED

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 4.0-Gbyte disk with a VTOC label displayed from the format utility:


Total disk cylinders available: 8892 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders        Size            Blocks
  0       root    wm    1110 - 4687        1.61GB    (0/3578/0) 3381210
  1       swap    wu       0 - 1109      512.00MB    (0/1110/0) 1048950
  2     backup    wm       0 - 8891        4.01GB    (0/8892/0) 8402940
  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 unassigned    wm       0               0         (0/0/0)          0
  7       home    wm    4688 - 8891        1.89GB    (0/4204/0) 3972780

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

Column Name 

Description 

Part

Partition (or slice number). See Table 32–7 for a description of this column.

Tag

Partition tag. See Table 32–7 for a description of this column.

Flags

Partition flag. See Table 32–7 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. 

First Sector 

EFI – The starting block number.

Last Sector 

EFI – The ending block number.

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


# prtvtoc /dev/rdsk/c4t1d0s0
* /dev/rdsk/c4t1d0s0 partition map
*
* Dimensions:
*     512 bytes/sector
* 2576941056 sectors
* 2576940989 accessible sectors
*
* Flags:
*   1: unmountable
*  10: read-only
*
*                           First     Sector    Last
* Partition  Tag  Flags     Sector     Count    Sector   Mount Directory
       0      2    00          34   629145600  629145633
       1      4    00   629145634   629145600 1258291233
       6      4    00  1258291234  1318633404 2576924637
       8     11    00  2576924638       16384 2576941021
* Flags:
*   1: unmountable
*  10: read-only
*

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 32–7.

Partition (or Slice) Table

This section contains the following information: 

Partition

Partition (or slice number). For a description of this column, see Table 32–7.

Tag

Partition tag. For a description of this column, see Table 32–7.

Flags

Partition flag. For a description of this column, see Table 32–7.

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.