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.
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. Table 21-7 describes partition table terminology.
Table 21-7 Partition Table Terminology
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.
The following partition table example is displayed from a 535-Mbyte disk using the format utility:
The partition table contains the following information:
Column Name |
Description |
---|---|
Part |
Partition (or slice number). See Table 21-7 for a description of this column. |
Tag |
Partition tag. See Table 21-7 for a description of this column. |
Flags |
Partition flag. See Table 21-7 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/c0t3d0s0 * /dev/rdsk/c0t3d0s0 partition map * * Dimensions: * 512 bytes/sector * 80 sectors/track * 9 tracks/cylinder * 720 sectors/cylinder * 2500 cylinders * 1151 accessible cylinders * * Flags: * 1: unmountable * 10: read-only * * First Sector Last * Partition Tag Flags Sector Count Sector Mount Directory 0 2 00 0 66240 66239 / 1 3 01 66240 131760 197999 2 5 00 0 828720 828719 3 0 00 198000 66240 264239 /export 4 0 00 264240 66240 330479 /export/swap 5 0 00 330480 72000 402479 /opt 6 4 00 402480 385200 787679 /usr 7 8 00 787680 41040 828719 /export/home # |
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 21-7 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 21-7 for a description of this column. |
Tag |
Partition tag. See Table 21-7 for a description of this column. |
Flags |
Partition flag. See Table 21-7 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. |