Chapter 3. Disk partitions

The hard disk stores information about the location and size of each disk partition in the partition table. Using information from the partition table, the operating system treats each partition as a logical disk. Some of the advantages of disk partitioning include:

To enable partitions on a device, format a block device with different types of partition tables. The following table compares the properties of different types of partition tables that you can create on a block device.

The GUID partition table (GPT) is a partitioning scheme based on the Globally Unique Identifier (GUID).

GPT deals with the limitations of the Mater Boot Record (MBR) partition table. The MBR partition table cannot address storage larger than 2 TiB, equal to approximately 2.2 TB. Instead, GPT supports hard disks with larger capacity. The maximum addressable disk size is 8 ZiB, when using 512 b sector drives, and 64 ZiB, when using 4096 b sector drives. In addition, by default, GPT supports creation of up to 128 primary partitions. Extend the maximum amount of primary partitions by allocating more space to the partition table.

GPT disks use logical block addressing (LBA) and a partition layout as follows:

Figure 3.1. Disk with a GUID Partition Table

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The partition table is stored at the very start of the disk, before any file system or user data. For a more clear example, the partition table is shown as being separate in the following diagrams.

Figure 3.2. Disk with MBR partition table

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As the previous diagram shows, the partition table is divided into four sections of four unused primary partitions. A primary partition is a partition on a hard disk drive that contains only one logical drive (or section). Each logical drive holds the information necessary to define a single partition, meaning that the partition table can define no more than four primary partitions.

Each partition table entry contains important characteristics of the partition:

The starting and ending points define the size and location of the partition on the disk. Some of the operating systems boot loaders use the active flag. That means that the operating system in the partition that is marked "active" is booted.

The type is a number that identifies the anticipated usage of a partition. Some operating systems use the partition type to:

The following diagram shows an example of a drive with a single partition. In this example, the first partition is labeled as DOS partition type:

Figure 3.3. Disk with a single partition

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To create additional partitions, if needed, set the type to extended.

An extended partition is similar to a disk drive. It has its own partition table, which points to one or more logical partitions, contained entirely within the extended partition. The following diagram shows a disk drive with two primary partitions, and one extended partition containing two logical partitions, along with some unpartitioned free space.

Figure 3.4. Disk with both two primary and an extended MBR partitions

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You can have only up to four primary or three primary partitions and one extended partition. There is no fixed limit to the number of logical partitions. As a limit in Linux to access partitions, a single disk drive allows maximum 60 partitions.

The table below shows a list of some of the most commonly used MBR partition types and hexadecimal numbers to represent them.

There are multiple ways to manage partition types:

On Red Hat Enterprise Linux 10 with parted 3.5, you can use the additional flags chromeos_kernel and bls_boot.

The parted utility optionally accepts a file system type argument while creating a partition. For a list of the required conditions, see Creating a partition with parted. Use the value to:

The argument does not modify the file system on the partition. It only differentiates between the supported flags and GUIDs.

The following file system types are supported:

Red Hat Enterprise Linux uses a file-based naming scheme, with file names in the form of /dev/xxyN.

Device and partition names consist of the following structure:

In Red Hat Enterprise Linux, each partition forms a part of the storage, necessary to support a single set of files and directories. Mounting a partition makes the storage of that partition available, starting at the specified directory known as a mount point.

For example, if partition /dev/sda5 is mounted on /usr/, it means that all files and directories under /usr/ physically reside on /dev/sda5. The file /usr/share/doc/FAQ/txt/Linux-FAQ resides on /dev/sda5, while the file /etc/gdm/custom.conf does not.

Continuing the example, it is also possible that one or more directories below /usr/ would be mount points for other partitions. For example, /usr/local/man/whatis resides on /dev/sda7, rather than on /dev/sda5, if /usr/local includes a mounted /dev/sda7 partition.