Storage Administration Guide

• To create an XFS file system, use the following command:

  # mkfs.xfs block_device

  • Replace block_device with the path to a block device. For example, /dev/sdb1, /dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or /dev/my-volgroup/my-lv.
  • In general, the default options are optimal for common use.
  • When using mkfs.xfs on a block device containing an existing file system, add the -f option to overwrite that file system.

1. Format the partition or LVM volume with the ext3 file system using the mkfs.ext3 utility:

   # mkfs.ext3 block_device

   • Replace block_device with the path to a block device. For example, /dev/sdb1, /dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or /dev/my-volgroup/my-lv.
2. Label the file system using the e2label utility:

   # e2label block_device volume_label

Procedure 4.1. Revert from ext3 to ext2

1. Unmount the partition by logging in as root and typing:

   # umount /dev/mapper/VolGroup00-LogVol02

2. Change the file system type to ext2 by typing the following command:

   # tune2fs -O ^has_journal /dev/mapper/VolGroup00-LogVol02

3. Check the partition for errors by typing the following command:

   # e2fsck -y /dev/mapper/VolGroup00-LogVol02

4. Then mount the partition again as ext2 file system by typing:

   # mount -t ext2 /dev/mapper/VolGroup00-LogVol02 /mount/point

   Replace /mount/point with the mount point of the partition.

   Note

   If a .journal file exists at the root level of the partition, delete it.

• To create an ext4 file system, use the following command:

  # mkfs.ext4 block_device

  • Replace block_device with the path to a block device. For example, /dev/sdb1, /dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or /dev/my-volgroup/my-lv.
  • In general, the default options are optimal for most usage scenarios.

Procedure 5.1. Backing up ext2, ext3, or ext4 File Systems

1. Back up configuration information, including the content of the /etc/fstab file and the output of the fdisk -l command. This is useful for restoring the partitions.
   To capture this information, run the sosreport or sysreport utilities. For more information about sosreport, see the What is a sosreport and how to create one in Red Hat Enterprise Linux 4.6 and later? Kdowledgebase article.
2. Depending on the role of the partition:
   • If the partition you are backing up is an operating system partition, boot your system into the rescue mode. See the Booting to Rescue Mode section of the System Administrator's Guide.
   • When backing up a regular, data partition, unmount it.
     Although it is possible to back up a data partition while it is mounted, the results of backing up a mounted data partition can be unpredictable.
     If you need to back up a mounted file system using the dump utility, do so when the file system is not under a heavy load. The more activity is happening on the file system when backing up, the higher the risk of backup corruption is.
3. Use the dump utility to back up the content of the partitions:

   # dump -0uf backup-file /dev/device

   Replace backup-file with a path to a file where you want the to store the backup. Replace device with the name of the ext4 partition you want to back up. Make sure that you are saving the backup to a directory mounted on a different partition than the partition you are backing up.

   Example 5.2. Backing up Multiple ext4 Partitions

   To back up the content of the /dev/sda1, /dev/sda2, and /dev/sda3 partitions into backup files stored in the /backup-files/ directory, use the following commands:

   # dump -0uf /backup-files/sda1.dump /dev/sda1
   # dump -0uf /backup-files/sda2.dump /dev/sda2
   # dump -0uf /backup-files/sda3.dump /dev/sda3

   To do a remote backup, use the ssh utility or configure a password-less ssh login. For more information on ssh and password-less login, see the Using the ssh Utility and Using Key-based Authentication sections of the System Administrator's Guide.
   For example, when using ssh:

   Example 5.3. Performing a Remote Backup Using ssh

   # dump -0u -f - /dev/device | ssh root@remoteserver.example.com dd of=backup-file

   Note that if using standard redirection, you must pass the -f option separately.

Procedure 5.2. Restoring ext2, ext3, or ext4 File Systems

1. If you are restoring an operating system partition, boot your system into Rescue Mode. See the Booting to Rescue Mode section of the System Administrator's Guide.
   This step is not required for ordinary data partitions.
2. Rebuild the partitions you want to restore by using the fdisk or parted utilites.
   If the partitions no longer exist, recreate them. The new partitions must be large enough to contain the restored data. It is important to get the start and end numbers right; these are the starting and ending sector numbers of the partitions obtained from the fdisk utility when backing up.
   For more information on modifying partitions, see Chapter 13, Partitions
3. Use the mkfs utility to format the destination partition:

   # mkfs.ext4 /dev/device

   Important

   Do not format the partition that stores your backup files.
4. If you created new partitions, re-label all the partitions so they match their entries in the /etc/fstab file:

   # e2label /dev/device label

5. Create temporary mount points and mount the partitions on them:

   # mkdir /mnt/device
   # mount -t ext4 /dev/device /mnt/device

6. Restore the data from backup on the mounted partition:

   # cd /mnt/device
   # restore -rf device-backup-file

   If you want to restore on a remote machine or restore from a backup file that is stored on a remote host, you can use the ssh utility. For more information on ssh, see the Using the ssh Utility section of the System Administrator's Guide.
   Note that you need to configure a password-less login for the following commands. For more information on setting up a password-less ssh login, see the Using Key-based Authentication section of the System Administrator's Guide.
   • To restore a partition on a remote machine from a backup file stored on the same machine:

     # ssh remote-address "cd /mnt/device && cat backup-file | /usr/sbin/restore -r -f -"

   • To restore a partition on a remote machine from a backup file stored on a different remote machine:

     # ssh remote-machine-1 "cd /mnt/device && RSH=/usr/bin/ssh /usr/sbin/restore -rf remote-machine-2:backup-file"

7. Reboot:

   # systemctl reboot

1. Start parted.
2. Use the following command to view the partition table:

   (parted) print

Procedure 13.1. Creating a Partition

1. Before creating a partition, boot into rescue mode, or unmount any partitions on the device and turn off any swap space on the device.
2. Start parted:

   # parted /dev/sda

   Replace /dev/sda with the device name on which you want to create the partition.
3. View the current partition table to determine if there is enough free space:

   (parted) print

   If there is not enough free space, you can resize an existing partition. For more information, see Section 13.5, “Resizing a Partition with fdisk”.
   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, see the appendix An Introduction to Disk Partitions in the Red Hat Enterprise Linux 7 Installation Guide.
4. To create partition:

   (parted) mkpart part-type name fs-type start end

   Replace part-type with with primary, logical, or extended as per your requirement.
   Replace name with partition-name; name is required for GPT partition tables.
   Replace fs-type with any one of btrfs, ext2, ext3, ext4, fat16, fat32, hfs, hfs+, linux-swap, ntfs, reiserfs, or xfs; fs-type is optional.
   Replace start end with the size in megabytes as per your requirement.
   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:

   (parted) mkpart primary 1024 2048

   Note

   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.
   The changes start taking place as soon as you press Enter, so review the command before executing to it.
5. View the partition table to confirm that the created partition is in the partition table with the correct partition type, file system type, and size using the following command:

   (parted) print

   Also remember the minor number of the new partition so that you can label any file systems on it.
6. Exit the parted shell:

   (parted) quit

7. Use the following command after parted is closed to make sure the kernel recognizes the new partition:

   # cat /proc/partitions 

Procedure 13.3. Remove a Partition

1. Before removing a partition, do one of the following:
   • Boot into rescue mode, or
   • Unmount any partitions on the device and turn off any swap space on the device.
2. Start the parted utility:

   # parted device

   Replace device with the device on which to remove the partition: for example, /dev/sda.
3. View the current partition table to determine the minor number of the partition to remove:

   (parted) print

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

   (parted) rm 3

   The changes start taking place as soon as you press Enter, so review the command before committing to it.
5. After removing the partition, use the print command to confirm that it is removed from the partition table:

   (parted) print

6. Exit from the parted shell:

   (parted) quit

7. Examine the content of the /proc/partitions file to make sure the kernel knows the partition is removed:

   # cat /proc/partitions

8. Remove the partition from the /etc/fstab file. Find the line that declares the removed partition, and remove it from the file.
9. Regenerate mount units so that your system registers the new /etc/fstab configuration:

   # systemctl daemon-reload

Procedure 13.4. Resizing a Partition

1. Unmount the device:

   # umount /dev/vda

2. Run fdisk disk_name. For example:

   # fdisk /dev/vda
   Welcome to fdisk (util-linux 2.23.2).
   
   Changes will remain in memory only, until you decide to write them. Be careful before using the write command.
   
   Command (m for help):
   

3. Use the p option to determine the line number of the partition to be deleted.

   Command (m for help): p
   Disk /dev/vda: 16.1 GB, 16106127360 bytes, 31457280 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes
   Disk label type: dos
   Disk identifier: 0x0006d09a
   
   Device    Boot      Start         End      Blocks   Id  System
   /dev/vda1   *        2048     1026047      512000   83  Linux
   /dev/vda2         1026048    31457279    15215616   8e  Linux LVM
   

4. Use the d option to delete a partition. If there is more than one partition available, fdisk prompts you to provide a number of the partition to delete:

   Command (m for help): d
   Partition number (1,2, default 2): 2
   Partition 2 is deleted
   

5. Use the n option to create a partition and follow the prompts. Allow enough space for any future resizing. The fdisk default behavior (press Enter) is to use all space on the device. You can specify the end of the partition by sectors, or specify a human-readable size by using +<size><suffix>, for example +500M, or +10G.
   Red Hat recommends using the human-readable size specification if you do not want to use all free space, as fdisk aligns the end of the partition with the physical sectors. If you specify the size by providing an exact number (in sectors), fdisk does not align the end of the partition.

   Command (m for help): n
   Partition type:
      p   primary (1 primary, 0 extended, 3 free)
      e   extended
   Select (default p): *Enter*
   Using default response p
   Partition number (2-4, default 2): *Enter*
   First sector (1026048-31457279, default 1026048): *Enter*
   Using default value 1026048
   Last sector, +sectors or +size{K,M,G} (1026048-31457279, default 31457279): +500M
   Partition 2 of type Linux and of size 500 MiB is set
   

6. Set the partition type to LVM:

   Command (m for help): t
   Partition number (1,2, default 2): *Enter*
   Hex code (type L to list all codes): 8e
   Changed type of partition 'Linux' to 'Linux LVM'
   

7. Write the changes with the w option when you are sure the changes are correct, as errors can cause instability with the selected partition.
8. Run e2fsck on the device to check for consistency:

   # e2fsck /dev/vda
   e2fsck 1.41.12 (17-May-2010)
   Pass 1:Checking inodes, blocks, and sizes
   Pass 2:Checking directory structure
   Pass 3:Checking directory connectivity
   Pass 4:Checking reference counts
   Pass 5:Checking group summary information
   ext4-1:11/131072 files (0.0% non-contiguous),27050/524128 blocks
   

9. Mount the device:

   # mount /dev/vda

Procedure 14.1. Creating a Snapper Configuration File

1. Create or choose either:
   • A thinly-provisioned logical volume with a Red Hat supported file system on top of it, or
   • A Btrfs subvolume.
2. Mount the file system.
3. Create the configuration file that defines this volume.
   For LVM2:

   # snapper -c config_name create-config -f "lvm(fs_type)" /mount-point

   For example, to create a configuration file called lvm_config on an LVM2 subvolume with an ext4 file system, mounted at /lvm_mount, use:

   # snapper -c lvm_config create-config -f "lvm(ext4)" /lvm_mount

   For Btrfs:

   # snapper -c config_name create-config -f btrfs /mount-point

   • The -c config_name option specifies the name of the configuration file.
   • The create-config tells snapper to create a configuration file.
   • The -f file_system tells snapper what file system to use; if this is omitted snapper will attempt to detect the file system.
   • The /mount-point is where the subvolume or thinly-provisioned LVM2 file system is mounted.
   Alternatively, to create a configuration file called btrfs_config, on a Btrfs subvolume that is mounted at /btrfs_mount, use:

   # snapper -c btrfs_config create-config -f btrfs /btrfs_mount