This procedure describes how to view the partition table on a block device using the parted utility.

This section provides an example output of the print command in the parted shell and describes fields in the output.

Model: ATA SAMSUNG MZNLN256 (scsi)
Disk /dev/sda: 256GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
 1      1049kB  269MB   268MB   primary   xfs          boot
 2      269MB   34.6GB  34.4GB  primary
 3      34.6GB  45.4GB  10.7GB  primary
 4      45.4GB  256GB   211GB   extended
 5      45.4GB  256GB   211GB   logical

This section lists key points to consider before creating, removing, or resizing partitions.

The maximum number of partitions

The number of partitions on a device is limited by the type of the partition table:

The maximum size of a partition

The size of a partition on a device is limited by the type of the partition table:

If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.

Size alignment

The parted utility enables you to specify partition size using multiple different suffixes:

This section compares the properties of different types of partition tables that you can create on a block device.

The diagrams in this chapter show the partition table as being separate from the actual disk. However, this is not entirely accurate. In reality, the partition table is stored at the very start of the disk, before any file system or user data, but for clarity, they are separate in the following diagrams.

Figure 10.1. Disk with MBR partition table

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

Each partition table entry contains several important characteristics of the partition:

The starting and ending points define the partition’s size and location on the disk. The "active" flag is used by some operating systems boot loaders. In other words, the operating system in the partition that is marked "active" is booted, in this case.

The type is a number that identifies the partition’s anticipated usage. Some operating systems use the partition type to denote a specific file system type, to flag the partition as being associated with a particular operating system, to indicate that the partition contains a bootable operating system, or some combination of the three.

The following diagram shows an example of a drive with single partition:

Figure 10.2. Disk with a single partition

The single partition in this example is labeled as DOS. This label shows the partition type, with DOS being one of the most common ones.

In case four partitions are insufficient for your needs, you can use extended partitions to create up additional partitions. You can do this by setting the type of partition to "Extended".

An extended partition is like a disk drive in its own right - it has its own partition table, which points to one or more partitions (now called logical partitions, as opposed to the four primary partitions), contained entirely within the extended partition itself. The following diagram shows a disk drive with one primary partition and one extended partition containing two logical partitions (along with some unpartitioned free space):

Figure 10.3. Disk with both a primary and an extended MBR partition

As this figure implies, there is a difference between primary and logical partitions - there can be only up to four primary and extended partitions, but there is no fixed limit to the number of logical partitions that can exist. However, due to the way in which partitions are accessed in Linux, no more than 15 logical partitions can be defined on a single disk drive.

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

The GUID Partition Table (GPT) is a partitioning scheme based on using Globally Unique Identifier (GUID). GPT was developed to cope with limitations of the MBR partition table, especially with the limited maximum addressable storage space of a disk. Unlike MBR, which is unable to address storage larger than 2 TiB (equivalent to approximately 2.2 TB), GPT is used with hard disks larger than this; the maximum addressable disk size is 2.2 ZiB. In addition, GPT, by default, supports creating up to 128 primary partitions. This number could be extended by allocating more space to the partition table.

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

Figure 10.4. Disk with a GUID Partition Table

This procedure describes how to format a block device with a partition table using the parted utility.

This section lists key points to consider before creating, removing, or resizing partitions.

The maximum number of partitions

The number of partitions on a device is limited by the type of the partition table:

The maximum size of a partition

The size of a partition on a device is limited by the type of the partition table:

If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.

Size alignment

The parted utility enables you to specify partition size using multiple different suffixes:

This section describes different attributes that specify the type of a partition.

Partition types or flags

The partition type, or flag, is used by a running system only rarely. However, the partition type matters to on-the-fly generators, such as systemd-gpt-auto-generator, which use the partition type to, for example, automatically identify and mount devices.

Partition file system type

The parted utility optionally accepts a file system type argument when creating a partition. The value is used to:

The argument does not modify the file system on the partition in any way. It only differentiates between the supported flags or 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 is used to form part of the storage necessary to support a single set of files and directories. This is done using the process known as mounting, which associates a partition with a directory. Mounting a partition makes its storage available starting at the specified directory, known as a mount point.

For example, if partition /dev/sda5 is mounted on /usr/, that would mean that all files and directories under /usr/ physically reside on /dev/sda5. So the file /usr/share/doc/FAQ/txt/Linux-FAQ would be stored on /dev/sda5, while the file /etc/gdm/custom.conf would not.

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

This procedure describes how to create a new partition on a block device using the parted utility.

This procedure describes how to set a partition type, or flag, using the fdisk utility.

This section lists key points to consider before creating, removing, or resizing partitions.

The maximum number of partitions

The number of partitions on a device is limited by the type of the partition table:

The maximum size of a partition

The size of a partition on a device is limited by the type of the partition table:

If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.

Size alignment

The parted utility enables you to specify partition size using multiple different suffixes:

This procedure describes how to remove a disk partition using the parted utility.

This section lists key points to consider before creating, removing, or resizing partitions.

The maximum number of partitions

The number of partitions on a device is limited by the type of the partition table:

The maximum size of a partition

The size of a partition on a device is limited by the type of the partition table:

If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.

Size alignment

The parted utility enables you to specify partition size using multiple different suffixes:

This procedure resizes a disk partition using the parted utility.

In this situation, the partitions that are already defined do not span the entire hard disk, leaving unallocated space that is not part of any defined partition. The following diagram shows what this might look like:

Figure 10.5. Disk with unpartitioned free space

In the previous example, the first diagram represents a disk with one primary partition and an undefined partition with unallocated space, and the second diagram represents a disk with two defined partitions with allocated space.

An unused hard disk also falls into this category. The only difference is that all the space is not part of any defined partition.

In any case, you can create the necessary partitions from the unused space. This scenario is mostly likely for a new disk. Most preinstalled operating systems are configured to take up all available space on a disk drive.

In this case, you can have one or more partitions that you no longer use. The following diagram illustrated such a situation.

Figure 10.6. Disk with an unused partition

In the previous example, the first diagram represents a disk with an unused partition, and the second diagram represents reallocating an unused partition for Linux.

In this situation, you can use the space allocated to the unused partition. You must delete the partition and then create the appropriate Linux partition(s) in its place. You can delete the unused partition and manually create new partitions during the installation process.

This is the most common situation. It is also the hardest to handle, because even if you have enough free space, it is presently allocated to a partition that is already in use. If you purchased a computer with preinstalled software, the hard disk most likely has one massive partition holding the operating system and data.

Aside from adding a new hard drive to your system, you can choose from destructive and non-destructive repartitioning.

10.6.3.1. Destructive repartitioning

This deletes the partition and creates several smaller ones instead. You must make a complete backup because any data in the original partition is destroyed. Create two backups, use verification (if available in your backup software), and try to read data from the backup before deleting the partition.

Warning

If an operating system was installed on that partition, it must be reinstalled if you want to use that system as well. Be aware that some computers sold with pre-installed operating systems might not include the installation media to reinstall the original operating system. You should check whether this applies to your system before you destroy your original partition and its operating system installation.

After creating a smaller partition for your existing operating system, you can reinstall software, restore your data, and start your Red Hat Enterprise Linux installation.

Figure 10.7. Destructive repartitioning action on disk

Warning

Any data previously present in the original partition is lost.

10.6.3.2. Non-destructive repartitioning

With non-destructive repartitioning you execute a program that makes a big partition smaller without losing any of the files stored in that partition. This method is usually reliable, but can be very time-consuming on large drives.

The non-destructive repartitioning process is straightforward and consist of three steps:

1. Compress and backup existing data
2. Resize the existing partition
3. Create new partition(s)

Each step is described further in more detail.

10.6.3.2.1. Compressing existing data

The first step is to compress the data in your existing partition. The reason for doing this is to rearrange the data to maximize the available free space at the "end" of the partition.

Figure 10.8. Compression on disk

In the previous example, the first diagram represents disk before compression, and the second diagram after compression.

This step is crucial. Without it, the location of the data could prevent the partition from being resized to the desired extent. Note that some data cannot be moved. In this case, it severely restricts the size of your new partitions, and you might be forced to destructively repartition your disk.

10.6.3.2.2. Resizing the existing partition

The following figure shows the actual resizing process. While the actual result of the resizing operation varies, depending on the software used, in most cases the newly freed space is used to create an unformatted partition of the same type as the original partition.

Figure 10.9. Partition resizing on disk

In the previous example, the first diagram represents partition before resizing, and the second diagram after resizing.

It is important to understand what the resizing software you use does with the newly freed space,so that you can take the appropriate steps. In the case illustrated here, it would be best to delete the new DOS partition and create the appropriate Linux partition or partitions.

10.6.3.2.3. Creating new partitions

As mentioned in the example Resizing the existing partition, it might or might not be necessary to create new partitions. However, unless your resizing software supports systems with Linux installed, it is likely that you must delete the partition that was created during the resizing process.

Figure 10.10. Disk with final partition configuration

In the previous example, the first diagram represents disk before configuration, and the second diagram after configuration.