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.
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.
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. |