Disk Partitions

Disk Partitions

Disks are divided into logical units called partitions. An example of a partitioned disk is shown in Figure 1-3. Partitions divide the disk into fixed-size portions which can be used by IRIX or by users for different purposes. Partition sizes are measured in 512-byte disk blocks. On SCSI disks, partitions merely need to be integral numbers of disk blocks. They can be an integral number of cylinders or a fractional number of cylinders.

Figure 1-3 : Disk Partitions Each disk block can belong to any number of partitions, including no partition (in which case the disk space of the cylinder is unused or wasted). This means that partitions can overlap. For example, a disk can be divided into several non-overlapping partitions and have an additional partition defined that is the entire disk.

Each partition on a disk has a number from 0 through 15. By convention, some of these partition numbers have a particular function and a name. These numbers, names, and functions are listed in Table 1-1.

Standard Partition Numbers, Names, and Functions
Partition Number Name Function
0 root Root partition, used for the Root filesystem on system disks.
1 swap Swap partition, used by IRIX for temporary storage when there is less physical memory than all of its processes need.
6 usr Usr partition, used on system disks when separate Root and Usr filesystems are used.
7 (none) The entire disk except the volume header and xfslog partition (if present).
8 volhdr Volume header (see the section "Volume Headers" in this chapter)
9 (none) Reserved partition (historically, this partition was the bad block partition on non-SCSI drives).
10 volume The entire disk, including the volume header.
15 xfslog A small partition used for an XFS log (see the section "Partition Types" in this chapter).

Standard Partition Numbers, Names, and Functions
Partition Number	Name	Function
0	root	Root partition, used for the Root filesystem on system disks.
1	swap	Swap partition, used by IRIX for temporary storage when there is less physical memory than all of its processes need.
6	usr	Usr partition, used on system disks when separate Root and Usr filesystems are used.
7	(none)	The entire disk except the volume header and xfslog partition (if present).
8	volhdr	Volume header (see the section "Volume Headers" in this chapter)
9	(none)	Reserved partition (historically, this partition was the bad block partition on non-SCSI drives).
10	volume	The entire disk, including the volume header.
15	xfslog	A small partition used for an XFS log (see the section "Partition Types" in this chapter).