Partitioning a Disk

The following information is described in this section:

Partition Table Terminology
Displaying Partition Table Information
Using the Free Hog Slice

The format utility is most often used by system administrators to partition a disk. The steps are as follows:

Determine which slices are needed.
Determine the size of each slice or partition.
Use the format utility to partition the disk.
Label the disk with new partition information.
Create the file system for each partition.

The easiest way to partition a disk is to use the modify command from the partition menu of the format utility. The modify command enables you to create partitions by specifying the size of each partition, without having to keep track of the starting cylinder boundaries. The modify command also keeps tracks of any disk space that remains in the “free hog” slice.

Partition Table Terminology

An important part of the disk label is the partition table. The partition table 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 7-3 Partition Table Terminology

Partition Term	Value	Description
Number	`0–7`	VTOC – Partitions or slices, numbered 0–7. EFI – Partitions 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 state is the default for 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 about displaying the partition table, see the following references:

Displaying Partition Table Information

The following format utility output shows an example of a partition table from a 74-GB disk with a VTOC label displayed:

Total disk cylinders available: 38756 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders         Size            Blocks
  0       root    wm       3 -  2083        4.00GB    (2081/0/0)    8390592
  1       swap    wu    2084 -  3124        2.00GB    (1041/0/0)    4197312
  2     backup    wm       0 - 38755       74.51GB    (38756/0/0) 156264192
  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    3125 - 38755       68.50GB    (35631/0/0) 143664192
  8       boot    wu       0 -     0        1.97MB    (1/0/0)          4032
  9 alternates    wu       1 -     2        3.94MB    (2/0/0)          8064

partition>

The partition table that is displayed by the format utility contains the following information.

Column Name	Description
`Part`	Partition or slice number. See Table 7-3 for a description of this column.
`Tag`	Partition tag. See Table 7-3 for a description of this column.
`Flag`	Partition flag. See Table 7-3 for a description of this column.
`Cylinders`	The starting and ending cylinder number for the slice. Not displayed on EFI-labeled disks.
`Size`	The slice or partition size in MB.
`Blocks`	The total number of cylinders and the total number of sectors per slice. Not displayed on EFI-labeled disks.
`First Sector`	EFI – The starting block number. Not displayed on VTOC-labeled disks.
`Last Sector`	EFI – The ending block number. Not displayed on VTOC-labeled disks.

The following is an example of an 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

The output of the prtvtoc command provides information in the following three sections:

Dimensions
Flags
Partition Table

`prtvtoc` Column Name	Description
`Partition`	Partition or slice number. For a description of this column, see Table 7-3.
`Tag`	Partition tag. For a description of this column, see Table 7-3.
`Flags`	Partition flag. For a description of this column, see Table 7-3.
`First Sector`	The first sector of the slice or partition.
`Sector Count`	The total number of sectors in the slice or partition.
`Last Sector`	The last sector of the slice or partition.
`Mount Directory`	The last mount point directory for the file system.

Using the Free Hog Slice

When you use the format utility to change the size of one or more disk slices, you designate a temporary slice that will expand and shrink to accommodate the resizing operations.

This temporary slice donates, or “frees,” space when you expand a slice, and receives, or “hogs,” the discarded space when you shrink a slice. For this reason, the donor slice is sometimes called the free hog.

The free hog slice exists only during installation or when you run the format utility. There is no permanent free hog slice during day-to-day operations.

For information on using the free hog slice, see SPARC: How to Create a Disk Slice for a ZFS Root File System or x86: How to Replace a ZFS Root Pool Disk (EFI (GPT)).

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