Which of the following commands creates a new logical volume in a volume group in Linux?

5.1 Understanding the logical volume manager

LVM enables flexible distribution of hard disk space over several physical volumes (hard disks, partitions, LUNs). It was developed because the need to change the segmentation of hard disk space might arise only after the initial partitioning has already been done during installation. Because it is difficult to modify partitions on a running system, LVM provides a virtual pool (volume group or VG) of storage space from which logical volumes (LVs) can be created as needed. The operating system accesses these LVs instead of the physical partitions. Volume groups can span more than one disk, so that several disks or parts of them can constitute one single VG. In this way, LVM provides a kind of abstraction from the physical disk space that allows its segmentation to be changed in a much easier and safer way than through physical repartitioning.

compares physical partitioning (left) with LVM segmentation (right). On the left side, one single disk has been divided into three physical partitions (PART), each with a mount point (MP) assigned so that the operating system can access them. On the right side, two disks have been divided into two and three physical partitions each. Two LVM volume groups (VG 1 and VG 2) have been defined. VG 1 contains two partitions from DISK 1 and one from DISK 2. VG 2 contains the remaining two partitions from DISK 2.

Figure 5.1: Physical partitioning versus LVM

In LVM, the physical disk partitions that are incorporated in a volume group are called physical volumes (PVs). Within the volume groups in , four logical volumes (LV 1 through LV 4) have been defined, which can be used by the operating system via the associated mount points (MP). The border between different logical volumes need not be aligned with any partition border. See the border between LV 1 and LV 2 in this example.

LVM features:

• Several hard disks or partitions can be combined in a large logical volume.

• Provided the configuration is suitable, an LV (such as

  > sudo pvs -o vg_name,lv_name,pv_name,seg_pe_ranges
  root's password:
    VG   LV    PV         PE Ranges
               /dev/sda1
    DATA DEVEL /dev/sda5  /dev/sda5:0-3839
    DATA       /dev/sda5
    DATA LOCAL /dev/sda6  /dev/sda6:0-2559
    DATA       /dev/sda7
    DATA       /dev/sdb1
    DATA       /dev/sdc1

  8) can be enlarged when the free space is exhausted.

• Using LVM, it is possible to add hard disks or LVs in a running system. However, this requires hotpluggable hardware that is capable of such actions.

• It is possible to activate a striping mode that distributes the data stream of a logical volume over several physical volumes. If these physical volumes reside on different disks, this can improve the reading and writing performance like RAID 0.

• The snapshot feature enables consistent backups (especially for servers) in the running system.

Note: LVM and RAID

Even though LVM also supports RAID levels 0, 1, 4, 5 and 6, we recommend using

> sudo pvs -o vg_name,lv_name,pv_name,seg_pe_ranges
root's password:
  VG   LV    PV         PE Ranges
             /dev/sda1
  DATA DEVEL /dev/sda5  /dev/sda5:0-3839
  DATA       /dev/sda5
  DATA LOCAL /dev/sda6  /dev/sda6:0-2559
  DATA       /dev/sda7
  DATA       /dev/sdb1
  DATA       /dev/sdc1

Warning: IBM Z: LVM root file system

If you configure the system with a root file system on LVM or software RAID array, you must place

> vgdisplay VG_NAME | grep "Total PE"

With these features, using LVM already makes sense for heavily-used home PCs or small servers. If you have a growing data stock, as in the case of databases, music archives, or user directories, LVM is especially useful. It allows file systems that are larger than the physical hard disk. However, keep in mind that working with LVM is different from working with conventional partitions.

You can manage new or existing LVM storage objects by using the YaST Partitioner. Instructions and further information about configuring LVM are available in the official LVM HOWTO.

5.2 Creating volume groups

An LVM volume group (VG) organizes the Linux LVM partitions into a logical pool of space. You can carve out logical volumes from the available space in the group. The Linux LVM partitions in a group can be on the same or different disks. You can add partitions or entire disks to expand the size of the group.

To use an entire disk, it must not contain any partitions. When using partitions, they must not be mounted. YaST will automatically change their partition type to

> vgdisplay VG_NAME | grep "Total PE"

1. Launch YaST and open the Partitioner.

2. In case you need to reconfigure your existing partitioning setup, proceed as follows. Refer to for details. Skip this step if you only want to use unused disks or partitions that already exist.

   Warning: Physical volumes on unpartitioned disks

   You can use an unpartitioned disk as a physical volume (PV) if that disk is not the one where the operating system is installed and from which it boots.

   As unpartitioned disks appear as unused at the system level, they can easily be overwritten or wrongly accessed.

   1. To use an entire hard disk that already contains partitions, delete all partitions on that disk.

   2. To use a partition that is currently mounted, unmount it.

3. In the left panel, select Volume Management.

   A list of existing Volume Groups opens in the right panel.

4. At the lower left of the Volume Management page, click Add Volume Group.

   

5. Define the volume group as follows:

   1. Specify the Volume Group Name.

      If you are creating a volume group at install time, the name

      > vgdisplay VG_NAME | grep "Total PE"

      2 is suggested for a volume group that will contain the SUSE Linux Enterprise Server system files.

   2. Specify the Physical Extent Size.

      The Physical Extent Size defines the size of a physical block in the volume group. All the disk space in a volume group is handled in chunks of this size. Values can be from 1 KB to 16 GB in powers of 2. This value is normally set to 4 MB.

      In LVM1, a 4 MB physical extent allowed a maximum LV size of 256 GB because it supports only up to 65534 extents per LV. LVM2, which is used on SUSE Linux Enterprise Server, does not restrict the number of physical extents. Having many extents has no impact on I/O performance to the logical volume, but it slows down the LVM tools.

      

      Important: Physical extent sizes

      Different physical extent sizes should not be mixed in a single VG. The extent should not be modified after the initial setup.

   3. In the Available Physical Volumes list, select the Linux LVM partitions that you want to make part of this volume group, then click Add to move them to the Selected Physical Volumes list.

   4. Click Finish.

      The new group appears in the Volume Groups list.

6. On the Volume Management page, click Next, verify that the new volume group is listed, then click Finish.

7. To check which physical devices are part of the volume group, open the YaST Partitioner at any time in the running system and click Volume Management › Edit › Physical Devices. Leave this screen with Abort.

   

   Figure 5.2: Physical volumes in the volume group named DATA

     

5.3 Creating logical volumes

A logical volume provides a pool of space similar to what a hard disk does. To make this space usable, you need to define logical volumes. A logical volume is similar to a regular partition—you can format and mount it.

Use The YaST Partitioner to create logical volumes from an existing volume group. Assign at least one logical volume to each volume group. You can create new logical volumes as needed until all free space in the volume group has been exhausted. An LVM logical volume can optionally be thinly provisioned, allowing you to create logical volumes with sizes that overbook the available free space (see for more information).

• Normal volume:  (Default) The volume’s space is allocated immediately.

• Thin pool:  The logical volume is a pool of space that is reserved for use with thin volumes. The thin volumes can allocate their needed space from it on demand.

• Thin volume:  The volume is created as a sparse volume. The volume allocates needed space on demand from a thin pool.

• Mirrored volume:  The volume is created with a defined count of mirrors.

Procedure 5.1: Setting up a logical volume

1. Launch YaST and open the Partitioner.

2. In the left panel, select Volume Management. A list of existing Volume Groups opens in the right panel.

3. Select the volume group in which you want to create the volume and choose Logical Volumes › Add Logical Volume.

4. Provide a Name for the volume and choose Normal Volume (refer to for setting up thinly provisioned volumes). Proceed with Next.

   

5. Specify the size of the volume and whether to use multiple stripes.

   Using a striped volume, the data will be distributed among several physical volumes. If these physical volumes reside on different hard disks, this generally results in a better reading and writing performance (like RAID 0). The maximum number of available stripes is equal to the number of physical volumes. The default (

   > vgdisplay VG_NAME | grep "Total PE"

   3 is to not use multiple stripes.
   

6. Choose a Role for the volume. Your choice here only affects the default values for the upcoming dialog. They can be changed in the next step. If in doubt, choose Raw Volume (Unformatted).

   

7. Under Formatting Options, select Format Partition, then select the File system. The content of the Options menu depends on the file system. Usually there is no need to change the defaults.

   Under Mounting Options, select Mount partition, then select the mount point. Click Fstab Options to add special mounting options for the volume.

8. Click Finish.

9. Click Next, verify that the changes are listed, then click Finish.

> vgdisplay VG_NAME | grep "Total PE"

> vgdisplay VG_NAME | grep "Total PE"

> vgdisplay VG_NAME | grep "Total PE"

> sudo lvcreate -L 500G -m 2 -n lv1 vg1

> vgdisplay VG_NAME | grep "Total PE"

> vgdisplay VG_NAME | grep "Total PE"

> vgdisplay VG_NAME | grep "Total PE"

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

5.4 Automatically activating non-root LVM volume groups

Activation behavior for non-root LVM volume groups is controlled in the

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

If you have defined a list in the auto_activation_volume_list parameter, the following will happen:

1. Each logical volume is first checked against this list.

2. If it does not match, the logical volume will not be activated.

By default, non-root LVM volume groups are automatically activated on system restart by Dracut. This parameter allows you to activate all volume groups on system restart, or to activate only specified non-root LVM volume groups.

5.5 Resizing an existing volume group

The space provided by a volume group can be expanded at any time in the running system without service interruption by adding physical volumes. This will allow you to add logical volumes to the group or to expand the size of existing volumes as described in .

It is also possible to reduce the size of the volume group by removing physical volumes. YaST only allows to remove physical volumes that are currently unused. To find out which physical volumes are currently in use, run the following command. The partitions (physical volumes) listed in the

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo pvs -o vg_name,lv_name,pv_name,seg_pe_ranges
root's password:
  VG   LV    PV         PE Ranges
             /dev/sda1
  DATA DEVEL /dev/sda5  /dev/sda5:0-3839
  DATA       /dev/sda5
  DATA LOCAL /dev/sda6  /dev/sda6:0-2559
  DATA       /dev/sda7
  DATA       /dev/sdb1
  DATA       /dev/sdc1

1. Launch YaST and open the Partitioner.

2. In the left panel, select Volume Management. A list of existing Volume Groups opens in the right panel.

3. Select the volume group you want to change, activate the Physical Volumes tab, then click Change.

   

4. Do one of the following:

   • Add:  Expand the size of the volume group by moving one or more physical volumes (LVM partitions) from the Available Physical Volumes list to the Selected Physical Volumes list.

   • Remove:  Reduce the size of the volume group by moving one or more physical volumes (LVM partitions) from the Selected Physical Volumes list to the Available Physical Volumes list.

5. Click Finish.

6. Click Next, verify that the changes are listed, then click Finish.

5.6 Resizing a logical volume

In case there is unused free space available in the volume group, you can enlarge a logical volume to provide more usable space. You may also reduce the size of a volume to free space in the volume group that can be used by other logical volumes.

Note: “Online” resizing

When reducing the size of a volume, YaST automatically resizes its file system, too. Whether a volume that is currently mounted can be resized “online” (that is while being mounted), depends on its file system. Growing the file system online is supported by Btrfs, XFS, Ext3, and Ext4.

Shrinking the file system online is only supported by Btrfs. To shrink the Ext2/3/4 file systems, you need to unmount them. Shrinking volumes formatted with XFS is not possible, since XFS does not support file system shrinking.

1. Launch YaST and open the Partitioner.

2. In the left panel, select Volume Management. A list of existing Volume Groups opens in the right panel.

3. Select the logical volume you want to change, then click Resize.

   

4. Set the intended size by using one of the following options:

   • Maximum size.  Expand the size of the logical volume to use all space left in the volume group.

   • Minimum size.  Reduce the size of the logical volume to the size occupied by the data and the file system metadata.

   • Custom size.  Specify the new size for the volume. The value must be within the range of the minimum and maximum values listed above. Use K, M, G, T for Kilobytes, Megabytes, Gigabytes and Terabytes (for example

     > sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

     2).

5. Click OK.

6. Click Next, verify that the change is listed, then click Finish.

5.7 Deleting a volume group or a logical volume

Warning: Data loss

Deleting a volume group destroys all of the data in each of its member partitions. Deleting a logical volume destroys all data stored on the volume.

1. Launch YaST and open the Partitioner.

2. In the left panel, select Volume Management. A list of existing volume groups opens in the right panel.

3. Select the volume group or the logical volume you want to remove and click Delete.

4. Depending on your choice, warning dialogs are shown. Confirm them with Yes.

5. Click Next, verify that the deleted volume group is listed—deletion is indicated by a red-colored font—then click Finish.

5.8 Disabling LVM on boot

If there is an error on the LVM storage, the scanning of LVM volumes may prevent entering the emergency/rescue shell. Thus, further problem diagnosis is not possible. To disable this scanning in case of an LVM storage failure, you can pass the

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

5.9 Using LVM commands

For information about using LVM commands, see the

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

LVM commands

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

Initializes a device (such as

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

Displays information about the LVM physical volume, such as whether it is currently being used in a logical volume.

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

Creates a clustered volume group with one or more specified devices.

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

Configures the mode of volume group activation. You can specify one of the following values:

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  7 - only the logical volumes that are not affected by missing physical volumes can be activated, even though the particular logical volume can tolerate such a failure.

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  8 - is the default activation mode. If there is a sufficient level of redundancy to activate a logical volume, the logical volume can be activated even though some physical volumes are missing.

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  9 - the LVM tries to activate the volume group even though some physical volumes are missing. If a non-redundant logical volume is missing important physical volumes, then the logical volume usually cannot be activated and is handled as an error target.

export DM_DISABLE_UDEV=1

Activates (

export DM_DISABLE_UDEV=1

export DM_DISABLE_UDEV=1

When activating a volume in a cluster, ensure that you use the

export DM_DISABLE_UDEV=1

export DM_DISABLE_UDEV=1

Removes a volume group. Before using this command, remove the logical volumes, then deactivate the volume group.

export DM_DISABLE_UDEV=1

Displays information about a specified volume group.

To find the total physical extent of a volume group, enter

> vgdisplay VG_NAME | grep "Total PE"

export DM_DISABLE_UDEV=1

Creates a logical volume of the specified size.

export DM_DISABLE_UDEV=1

Creates a thin pool named

export DM_DISABLE_UDEV=1

The following example creates a thin pool with a size of 5 GB from the volume group

export DM_DISABLE_UDEV=1

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvextend -L +SIZE /dev/VG_NAME/LV_NAME

Creates a thin logical volume within the pool POOL_NAME. The following example creates a 1GB thin volume named

> sudo lvextend -L +SIZE /dev/VG_NAME/LV_NAME

export DM_DISABLE_UDEV=1

export DM_DISABLE_UDEV=1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvextend -L +SIZE /dev/VG_NAME/LV_NAME

It is also possible to combine thin pool and thin logical volume creation in one command:

> sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

> sudo lvextend -L +SIZE /dev/VG_NAME/LV_NAME

Configures the mode of logical volume activation. You can specify one of the following values:

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  7 - the logical volume can be activated only if all its physical volumes are active.

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  8 - is the default activation mode. If there is a sufficient level of redundancy to activate a logical volume, the logical volume can be activated even though some physical volumes are missing.

• > sudo lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1

  9 - the LVM tries to activate the volume even though some physical volumes are missing. In this case part of the logical volume may be unavailable and it might cause data loss. This option is typically not used, but might be useful when restoring data.

You can specify the activation mode also in

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Creates a snapshot volume for the specified logical volume. If the size option (

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Removes a logical volume.

Before using this command, close the logical volume by unmounting it with the

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Removes a snapshot volume.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Reverts the logical volume to the version of the snapshot.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Adds the specified device (physical volume) to an existing volume group.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Removes a specified physical volume from an existing volume group.

Ensure that the physical volume is not currently being used by a logical volume. If it is, you must move the data to another physical volume by using the

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Extends the size of a specified logical volume. Afterward, you must also expand the file system to take advantage of the newly available space. See Chapter 2, Resizing file systems for details.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Reduces the size of a specified logical volume.

Ensure that you reduce the size of the file system first before shrinking the volume, otherwise you risk losing data. See Chapter 2, Resizing file systems for details.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

Renames an existing LVM logical volume. It does not change the volume group name.

Tip: Bypassing udev on volume creation

In case you want to manage LV device nodes and symbolic links by using LVM instead of by using udev rules, you can achieve this by disabling notifications from udev with one of the following methods:

• Configure

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  14 and

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  15 in

  > sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

  0.

  Note that specifying

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  17 with the

  > vgdisplay VG_NAME | grep "Total PE"

  6 command has the same effect as

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  15; setting

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  14 is still required.

• Setting the environment variable

  > sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

  21:

  export DM_DISABLE_UDEV=1

  This will also disable notifications from udev. In addition, all udev related settings from

  > sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

  0 will be ignored.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

5.10 Tagging LVM2 storage objects

A tag is an unordered keyword or term assigned to the metadata of a storage object. Tagging allows you to classify collections of LVM storage objects in ways that you find useful by attaching an unordered list of tags to their metadata.

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -L 5G --thinpool myPool LOCAL

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1

> sudo lvcreate -T LOCAL/myPool -V 1G -n myThin1