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Chapter 12. Managing Disk Storage

Introduction to different methods........

12.1. Standard Partitions using parted

Many users need to view the existing partition table, change the size of the partitions, remove partitions, or add partitions from free space or additional hard drives. The utility parted allows users to perform these tasks. This chapter discusses how to use parted to perform file system tasks.

If you want to view the system's disk space usage or monitor the disk space usage, refer to Section 40.3 File Systems.

You must have the parted package installed to use the parted utility. To start parted, at a shell prompt as root, type the command parted /dev/sda, where /dev/sda is the device name for the drive you want to configure. The (parted) prompt is displayed. Type help to view a list of available commands.

If you want to create, remove, or resize a partition, the device cannot be in use (partitions cannot be mounted, and swap space cannot be enabled). The partition table should not be modified while in use because the kernel may not properly recognize the changes. Data could be overwritten by writing to the wrong partition because the partition table and partitions mounted do not match. The easiest way to achieve this it to boot your system in rescue mode. Refer to Chapter 5 Basic System Recovery for instructions on booting into rescue mode. When prompted to mount the file system, select Skip.

Alternately, if the drive does not contain any partitions in use (system processes that use or lock the file system from being unmounted), you can unmount them with the umount command and turn off all the swap space on the hard drive with the swapoff command.

Table 12-1 contains a list of commonly used parted commands. The sections that follow explain some of them in more detail.

CommandDescription
check minor-numPerform a simple check of the file system
cp from toCopy file system from one partition to another; from and to are the minor numbers of the partitions
helpDisplay list of available commands
mklabel labelCreate a disk label for the partition table
mkfs minor-num file-system-typeCreate a file system of type file-system-type
mkpart part-type fs-type start-mb end-mbMake a partition without creating a new file system
mkpartfs part-type fs-type start-mb end-mbMake a partition and create the specified file system
move minor-num start-mb end-mbMove the partition
name minor-num nameName the partition for Mac and PC98 disklabels only
printDisplay the partition table
quitQuit parted
rescue start-mb end-mbRescue a lost partition from start-mb to end-mb
resize minor-num start-mb end-mbResize the partition from start-mb to end-mb
rm minor-numRemove the partition
select deviceSelect a different device to configure
set minor-num flag stateSet the flag on a partition; state is either on or off

Table 12-1. parted commands

12.1.1. Viewing the Partition Table

After starting parted, type the following command to view the partition table:

print

A table similar to the following appears:

Disk geometry for /dev/sda: 0.000-8678.789 megabytes
Disk label type: msdos
Minor    Start       End     Type      Filesystem  Flags
1          0.031    101.975  primary   ext3        boot
2        101.975   5098.754  primary   ext3
3       5098.755   6361.677  primary   linux-swap
4       6361.677   8675.727  extended
5       6361.708   7357.895  logical   ext3


Disk geometry for /dev/hda: 0.000-9765.492 megabytes
Disk label type: msdos
Minor    Start       End     Type      Filesystem  Flags
1          0.031    101.975  primary   ext3        boot
2        101.975    611.850  primary   linux-swap  
3        611.851    760.891  primary   ext3        
4        760.891   9758.232  extended              lba
5        760.922   9758.232  logical   ext3        

The first line displays the size of the disk, the second line displays the disk label type, and the remaining output shows the partition table.

In the partition table, the Minor number is the partition number. For example, the partition with minor number 1 corresponds to /dev/sda1. The Start and End values are in megabytes. The Type is one of primary, extended, or logical. The Filesystem is the file system type, which can be one of ext2, ext3, fat16, fat32, hfs, jfs, linux-swap, ntfs, reiserfs, hp-ufs, sun-ufs, or xfs. The Flags column lists the flags set for the partition. Available flags are boot, root, swap, hidden, raid, lvm, or lba.

In this example, minor number 1 refers to the /boot/ file system, minor number 2 refers to the root file system (/), minor number 3 refers to the swap, and minor number 5 refers to the /home/ file system.

TipTip
 

To select a different device without having to restart parted, use the select command followed by the device name such as /dev/sda. Then, you can view its partition table or configure it.

12.1.2. Creating a Partition

WarningWarning
 

Do not attempt to create a partition on a device that is in use.

Before creating a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to create the partition:

parted /dev/sda

View the current partition table to determine if there is enough free space:

print

If there is not enough free space, you can resize an existing partition. Refer to Section 12.1.4 Resizing a Partition for details.

12.1.2.1. Making the Partition

From the partition table, determine the start and end points of the new partition and what partition type it should be. You can only have four primary partitions (with no extended partition) on a device. If you need more than four partitions, you can have three primary partitions, one extended partition, and multiple logical partitions within the extended. For an overview of disk partitions, refer to the appendix An Introduction to Disk Partitions in the Red Hat Enterprise Linux Installation Guide.

For example, to create a primary partition with an ext3 file system from 1024 megabytes until 2048 megabytes on a hard drive type the following command:

mkpart primary ext3 1024 2048

TipTip
 

If you use the mkpartfs command instead, the file system is created after the partition is created. However, parted does not support creating an ext3 file system. Thus, if you wish to create an ext3 file system, use mkpart and create the file system with the mkfs command as described later. mkpartfs works for file system type linux-swap.

The changes start taking place as soon as you press [Enter], so review the command before executing to it.

After creating the partition, use the print command to confirm that it is in the partition table with the correct partition type, file system type, and size. Also remember the minor number of the new partition so that you can label it. You should also view the output of

cat /proc/partitions

to make sure the kernel recognizes the new partition.

12.1.2.2. Formating the Partition

The partition still does not have a file system. Create the file system:

/sbin/mkfs -t ext3 /dev/sda6

WarningWarning
 

Formatting the partition permanently destroys any data that currently exists on the partition.

12.1.2.3. Labeling the Partition

Next, give the partition a label. For example, if the new partition is /dev/sda6 and you want to label it /work:

e2label /dev/sda6 /work

By default, the installation program uses the mount point of the partition as the label to make sure the label is unique. You can use any label you want.

12.1.2.4. Creating the Mount Point

As root, create the mount point:

mkdir /work

12.1.2.5. Add to /etc/fstab

As root, edit the /etc/fstab file to include the new partition. The new line should look similar to the following:

LABEL=/work           /work                 ext3    defaults        1 2

The first column should contain LABEL= followed by the label you gave the partition. The second column should contain the mount point for the new partition, and the next column should be the file system type (for example, ext3 or swap). If you need more information about the format, read the man page with the command man fstab.

If the fourth column is the word defaults, the partition is mounted at boot time. To mount the partition without rebooting, as root, type the command:

mount /work

12.1.3. Removing a Partition

WarningWarning
 

Do not attempt to remove a partition on a device that is in use.

Before removing a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to remove the partition:

parted /dev/sda

View the current partition table to determine the minor number of the partition to remove:

print

Remove the partition with the command rm. For example, to remove the partition with minor number 3:

rm 3

The changes start taking place as soon as you press [Enter], so review the command before committing to it.

After removing the partition, use the print command to confirm that it is removed from the partition table. You should also view the output of

cat /proc/partitions

to make sure the kernel knows the partition is removed.

The last step is to remove it from the /etc/fstab file. Find the line that declares the removed partition, and remove it from the file.

12.1.4. Resizing a Partition

WarningWarning
 

Do not attempt to resize a partition on a device that is in use.

Before resizing a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to resize the partition:

parted /dev/sda

View the current partition table to determine the minor number of the partition to resize as well as the start and end points for the partition:

print

WarningWarning
 

The used space of the partition to resize must not be larger than the new size.

To resize the partition, use the resize command followed by the minor number for the partition, the starting place in megabytes, and the end place in megabytes. For example:

resize 3 1024 2048

After resizing the partition, use the print command to confirm that the partition has been resized correctly, is the correct partition type, and is the correct file system type.

After rebooting the system into normal mode, use the command df to make sure the partition was mounted and is recognized with the new size.

 
 
  Published under the terms of the GNU General Public License Design by Interspire