LVM - ArchWiki

# LVM

From ArchWiki

Related articles

- Software RAID and LVM
- dm-crypt/Encrypting an entire system#LVM on LUKS
- dm-crypt/Encrypting an entire system#LUKS on LVM
- Resizing LVM-on-LUKS
- Create root filesystem snapshots with LVM

From Wikipedia:Logical Volume Manager (Linux):

  LVM is a logical volume manager for the Linux kernel; it manages disk drives and similar mass-storage devices.

## LVM Building Blocks

Logical Volume Management utilizes the kernel's device-mapper feature to provide a system of partitions independent of underlying disk layout. With LVM you abstract your storage and have "virtual partitions", making extending/shrinking easier (subject to potential filesystem limitations).

Virtual partitions allow addition and removal without worry of whether you have enough contiguous space on a particular disk, getting caught up fdisking a disk in use (and wondering whether the kernel is using the old or new partition table), or, having to move other partitions out of the way. This is strictly an ease-of-management solution: LVM adds no security.

Basic building blocks of LVM:

Physical volume (PV)
  Partition on hard disk (or even the disk itself or loopback file) on which you can have volume groups. It has a special header and is divided into physical extents. Think of physical volumes as big building blocks used to build your hard drive.
Volume group (VG)
  Group of physical volumes used as a storage volume (as one disk). They contain logical volumes. Think of volume groups as hard drives.
Logical volume (LV)
  A "virtual/logical partition" that resides in a volume group and is composed of physical extents. Think of logical volumes as normal partitions.
Physical extent (PE)
  The smallest size in the physical volume that can be assigned to a logical volume (default 4MiB). Think of physical extents as parts of disks that can be allocated to any partition.

Example:

    Physical disks

      Disk1 (/dev/sda):
         _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
        |Partition1 50GB (Physical volume) |Partition2 80GB (Physical volume)     |
        |/dev/sda1                         |/dev/sda2                             |
        |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |

      Disk2 (/dev/sdb):
         _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
        |Partition1 120GB (Physical volume)                 |
        |/dev/sdb1                                          |
        | _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _|

    LVM logical volumes

      Volume Group1 (/dev/MyStorage/ = /dev/sda1 + /dev/sda2 + /dev/sdb1):
         _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
        |Logical volume1 15GB  |Logical volume2 35GB      |Logical volume3 200GB               |
        |/dev/MyStorage/rootvol|/dev/MyStorage/homevol    |/dev/MyStorage/mediavol             |
        |_ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |

## Advantages

LVM gives you more flexibility than just using normal hard drive partitions:

- Use any number of disks as one big disk.
- Have logical volumes stretched over several disks.
- Create small logical volumes and resize them "dynamically" as they get filled up.
- Resize logical volumes regardless of their order on disk. It does not depend on the position of the LV within VG, there is no need to ensure surrounding available space.
- Resize/create/delete logical and physical volumes online. File systems on them still need to be resized, but some (such as ext4) support online resizing.
- Online/live migration of LV being used by services to different disks without having to restart services.
- Snapshots allow you to backup a frozen copy of the file system, while keeping service downtime to a minimum.
- Support for various device-mapper targets, including transparent filesystem encryption and caching of frequently used data. This allows creating a system with (one or more) physical disks (encrypted with LUKS) and LVM on top to allow for easy resizing and management of separate volumes for /, /home,/backup, etc. without the hassle of entering a key multiple times on boot.

## Disadvantages

- Additional steps in setting up the system, more complicated.
- If dual-booting, note that Windows does not support LVM; you will be unable to access any LVM partitions from Windows.

## Installing Arch Linux on LVM

You should create your LVM Volumes between the partitioning and formatting steps of the installation procedure. Instead of directly formatting a partition to be your root file system, the file system will be created inside a logical volume (LV).

Make sure the lvm2 package is installed.

Quick overview:

- Create partition(s) where your PV(s) will reside. Set the partition type to 'Linux LVM', which is 8e if you use MBR, 8e00 for GPT.
- Create your physical volumes (PVs). If you have one disk it is best to just create one PV in one large partition. If you have multiple disks you can create partitions on each of them and create a PV on each partition.
- Create your volume group (VG) and add all PVs to it.
- Create logical volumes (LVs) inside that VG.
- Continue with Installation guide#Format the partitions.
- When you reach the “Create initial ramdisk environment” step in the Installation guide, add the `lvm` hook to `/etc/mkinitcpio.conf` (see below for details).

Warning: `/boot` cannot reside in LVM when using a boot loader which does not support LVM, you must create a separate `/boot` partition and format it directly. Only GRUB is known to support LVM.

### Create partitions

If LVM has to be set on the entire disk, there is no need to create any partitions.

Otherwise, partition the device as required before configuring LVM.

### Create physical volumes

To list all your devices capable of being used as a physical volume:

    # lvmdiskscan

Warning: Make sure you target the correct device, or below commands will result in data loss!

Create a physical volume on them:

    # pvcreate DEVICE

This command creates a header on each device so it can be used for LVM. As defined in #LVM Building Blocks, DEVICE can be a disk (e.g. `/dev/sda`), a partition (e.g. `/dev/sda2`) or a loop back device. For example:

    # pvcreate /dev/sda2

You can track created physical volumes with:

    # pvdisplay

Note: If using a SSD without partitioning it first, use `pvcreate --dataalignment 1m /dev/sda` (for erase block size < 1MiB), see e.g. here

### Create volume group

The next step is to create a volume group on this physical volume.

First you need to create a volume group on one of the physical volumes:

    # vgcreate <volume_group> <physical_volume>

For example:

    # vgcreate VolGroup00 /dev/sda2

Then add to it all other physical volumes you want to have in it:

    # vgextend <volume_group> <physical_volume>
    # vgextend <volume_group> <another_physical_volume>
    # ...

For example:

    # vgextend VolGroup00 /dev/sdb1
    # vgextend VolGroup00 /dev/sdc

You can track how your volume group grows with:

    # vgdisplay

Note: You can create more than one volume group if you need to, but then you will not have all your storage presented as one disk.

### Create in one step

LVM allows you to combine the creation of a volume group and the physical volumes in one easy step. For example, to create the group VolGroup00 with the three devices mentioned above, you can run:

    # vgcreate VolGroup00 /dev/sda2 /dev/sdb1 /dev/sdc

This command will first set up the three partitions as physical volumes (if necessary) and then create the volume group with the three volumes. The command will warn you it detects an existing filesystem on any of the devices.

### Create logical volumes

Tip: If you wish to use snapshots, logical volume caching, thin provisioned logical volumes or RAID see #Logical volume types.

Now we need to create logical volumes on this volume group. You create a logical volume with the next command by giving the name of a new logical volume, its size, and the volume group it will live on:

    # lvcreate -L <size> <volume_group> -n <logical_volume>

For example:

    # lvcreate -L 10G VolGroup00 -n lvolhome

This will create a logical volume that you can access later with `/dev/mapper/Volgroup00-lvolhome` or `/dev/VolGroup00/lvolhome`. Same as with the volume groups, you can use any name you want for your logical volume when creating it.

You can also specify one or more physical volumes to restrict where LVM allocates the data. For example, you may wish to create a logical volume for the root filesystem on your small SSD, and your home volume on a slower mechanical drive. Simply add the physical volume devices to the command line, for example:

    # lvcreate -L 10G VolGroup00 -n lvolhome /dev/sdc1

If you want to fill all the free space left on a volume group, use the next command:

    # lvcreate -l 100%FREE  <volume_group> -n <logical_volume>

You can track created logical volumes with:

    # lvdisplay

Note: You may need to load the device-mapper kernel module (`modprobe dm_mod'`) for the above commands to succeed.
Tip: You can start out with relatively small logical volumes and expand them later if needed. For simplicity, leave some free space in the volume group so there is room for expansion.

### Create file systems and mount logical volumes

Your logical volumes should now be located in `/dev/mapper/` and `/dev/YourVolumeGroupName`. If you cannot find them, use the next commands to bring up the module for creating device nodes and to make volume groups available:

    # modprobe dm_mod
    # vgscan
    # vgchange -ay

Now you can create file systems on logical volumes and mount them as normal partitions (if you are installing Arch linux, refer to mounting the partitions for additional details):

    # mkfs.<fstype> /dev/mapper/<volume_group>-<logical_volume>
    # mount /dev/mapper/<volume_group>-<logical_volume> /<mountpoint>

For example:

    # mkfs.ext4 /dev/mapper/VolGroup00-lvolhome
    # mount /dev/mapper/VolGroup00-lvolhome /home

Warning: When choosing mountpoints, just select your newly created logical volumes (use: `/dev/mapper/Volgroup00-lvolhome`). Do not select the actual partitions on which logical volumes were created (do not use: `/dev/sda2`).

### Configure mkinitcpio

In case your root filesystem is on LVM, you will need to enable the appropriate mkinitcpio hooks, otherwise your system might not boot. Enable:

- `udev` and `lvm2` for the default busybox based initramfs
- `systemd` and `sd-lvm2` for systemd based initramfs

`udev` is there by default. Edit the file and insert `lvm2` between `block` and `filesystems` like so:

    /etc/mkinitcpio.conf

    HOOKS=(base udev ... block lvm2 filesystems)

For systemd based initramfs:

    /etc/mkinitcpio.conf

    HOOKS=(base systemd ... block sd-lvm2 filesystems)

Afterwards, you can continue in normal installation instructions with the create an initial ramdisk step.

Tip:

- The `lvm2` and `sd-lvm2` hooks are installed by lvm2, not mkinitcpio. If you are running mkinitcpio in an arch-chroot for a new installation, lvm2 must be installed inside the arch-chroot for mkinitcpio to find the `lvm2` or `sd-lvm2` hook. If lvm2 only exists outside the arch-chroot, mkinitcpio will output `Error: Hook 'lvm2' cannot be found`.
- If your root filesystem is on LVM RAID see #Configure mkinitcpio for RAID.

### Kernel options

If the root file system resides in a logical volume, the `root=` kernel parameter must be pointed to the mapped device, e.g `/dev/mapper/vg-name-lv-name`.

## Volume operations

### Advanced options

If you need monitoring (needed for snapshots) you can enable lvmetad. For this set `use_lvmetad = 1` in `/etc/lvm/lvm.conf`. This is the default by now.

You can restrict the volumes that are activated automatically by setting the `auto_activation_volume_list` in `/etc/lvm/lvm.conf`. If in doubt, leave this option commented out.

### Resizing volumes

#### Physical volumes

After extending or prior to reducing the size of a device that has a physical volume on it, you need to grow or shrink the PV using `pvresize`.

##### Growing

To expand the PV on `/dev/sda1` after enlarging the partition, run:

    # pvresize /dev/sda1

This will automatically detect the new size of the device and extend the PV to its maximum.

Note: This command can be done while the volume is online.

##### Shrinking

To shrink a physical volume prior to reducing its underlying device, add the `--setphysicalvolumesize size` parameters to the command, e.g.:

    # pvresize --setphysicalvolumesize 40G /dev/sda1

The above command may leave you with this error:

     /dev/sda1: cannot resize to 25599 extents as later ones are allocated.
     0 physical volume(s) resized / 1 physical volume(s) not resized

Indeed `pvresize` will refuse to shrink a PV if it has allocated extents after where its new end would be. One needs to run pvmove beforehand to relocate these elsewhere in the volume group if there is sufficient free space.

###### Move physical extents

Before moving free extents to the end of the volume, one must run `# pvdisplay -v -m` to see physical segments. In the below example, there is one physical volume on `/dev/sdd1`, one volume group `vg1` and one logical volume `backup`.

    # pvdisplay -v -m

        Finding all volume groups.
        Using physical volume(s) on command line.
      --- Physical volume ---
      PV Name               /dev/sdd1
      VG Name               vg1
      PV Size               1.52 TiB / not usable 1.97 MiB
      Allocatable           yes
      PE Size               4.00 MiB
      Total PE              399669
      Free PE               153600
      Allocated PE          246069
      PV UUID               MR9J0X-zQB4-wi3k-EnaV-5ksf-hN1P-Jkm5mW

      --- Physical Segments ---
      Physical extent 0 to 153600:
        FREE
      Physical extent 153601 to 307199:
        Logical volume	/dev/vg1/backup
        Logical extents	1 to 153599
      Physical extent 307200 to 307200:
        FREE
      Physical extent 307201 to 399668:
        Logical volume	/dev/vg1/backup
        Logical extents	153601 to 246068

One can observe FREE space are split across the volume. To shrink the physical volume, we must first move all used segments to the beginning.

Here, the first free segment is from 0 to 153600 and leaves us with 153601 free extents. We can now move this segment number from the last physical extent to the first extent. The command will thus be:

    # pvmove --alloc anywhere /dev/sdd1:307201-399668 /dev/sdd1:0-92466

    /dev/sdd1: Moved: 0.1 %
    /dev/sdd1: Moved: 0.2 %
    ...
    /dev/sdd1: Moved: 99.9 %
    /dev/sdd1: Moved: 100,0%

Note:

- this command moves 92468 PEs (399668-307200) from the last segment to the first segment. This is possible as the first segment encloses 153600 free PEs, which can contain the 92467 moved PEs.
- the `--alloc anywhere` option is used as we move PEs inside the same partition. In case of different partitions, the command would look something like this: `# pvmove /dev/sdb1:1000-1999 /dev/sdc1:0-999`
- this command may take a long time (one to two hours) in case of large volumes. It might be a good idea to run this command in a Tmux or GNU Screen session. Any unwanted stop of the process could be fatal.
- once the operation is complete, run fsck to make sure your file system is valid.

###### Resize physical volume

Once all your free physical segments are on the last physical extent, run `# vgdisplay` and see your free PE.

Then you can now run again the command:

    # pvresize --setphysicalvolumesize size PhysicalVolume

See the result:

    # pvs

      PV         VG   Fmt  Attr PSize    PFree
      /dev/sdd1  vg1  lvm2 a--     1t     500g

###### Resize partition

Last, you need to shrink the partition with your favorite partitioning tool.

#### Logical volumes

Note: lvresize provides more or less the same options as the specialized `lvextend` and `lvreduce` commands, while allowing to do both types of operation. Notwithstanding this, all those utilities offer a `-r, --resizefs` option which allows to resize the file system together with the LV using fsadm(8) (ext2, ext3, ext4, ReiserFS and XFS supported). Therefore it may be easier to simply use `lvresize` for both operations and use `--resizefs` to simplify things a bit, except if you have specific needs or want full control over the process.

##### Growing or shrinking with lvresize

Warning: While enlarging a file system can often be done on-line (i.e. while it is mounted), even for the root partition, shrinking will nearly always require to first unmount the file system so as to prevent data loss. Make sure your FS supports what you are trying to do.

Extend logical volume lv1 within volume group vg1 by 2GB without touching its file system:

    # lvresize -L +2G vg1/lv1

Reduce the size of `vg1/lv1` by 500MB without resizing its file system (make sure it is already shrunk in that case):

    # lvresize -L -500M vg1/lv1

Set `vg1/lv1` to 15GB and resize its file system all at once:

    # lvresize -L 15G -r vg1/lv1

Note: Only ext2, ext3, ext4, ReiserFS and XFS file systems are supported. For a different type of file system look for the appropriate utility.

If you want to fill all the free space on a volume group, use the following command:

    # lvresize -l +100%FREE vg/lv

See lvresize(8) for more detailed options.

##### Extending the logical volume and file system in one go

This article or section is a candidate for merging with #Growing or shrinking with lvresize.

Notes: No need to split the sections. (Discuss in Talk:LVM#)
Warning: Not all file systems support resizing without loss of data and/or resizing online.

Extend the logical volume home in volume-group with 10GB

    # lvresize -L +10G /dev/volume-group/home --resize-fs

Alternatively with a XFS filesystem

    # lvextend -L+10G /dev/volume-group/home
    # xfs_growfs /home

Note: xfs_growfs takes a mount point as argument. See xfs_growfs(8) for more detailed options.

##### Resizing the file system separately

This article or section is a candidate for moving to Ext4.

Notes: File system specific operations should be placed in their respective wiki pages. (Discuss in Talk:LVM#)

If not using the `-r, --resizefs` option to `lv{resize,extend,reduce}` or using a file system unsupported by fsadm(8) (Btrfs, ZFS...), you need to manually resize the FS before shrinking the LV or after expanding it.

Warning: Not all file systems support resizing without loss of data and/or resizing online.

For example with an ext2/ext3/ext4 file system:

    # resize2fs vg/lv

will expand the FS to the maximum size of the underlying LV, while

    # resize2fs -M vg/lv

will shrink it to its minimum size. To resize it to a specified size, use:

    # resize2fs vg/lv NewSize

### Remove logical volume

Warning: Before you remove a logical volume, make sure to move all data that you want to keep somewhere else; otherwise, it will be lost!

First, find out the name of the logical volume you want to remove. You can get a list of all logical volumes with:

    # lvs

Next, look up the mountpoint of the chosen logical volume:

    $ lsblk

Then unmount the filesystem on the logical volume:

    # umount /<mountpoint>

Finally, remove the logical volume:

    # lvremove <volume_group>/<logical_volume>

For example:

    # lvremove VolGroup00/lvolhome

Confirm by typing in `y`.

Update `/etc/fstab` as necessary.

You can verify the removal of the logical volume by typing `lvs` as root again (see first step of this section).

### Add physical volume to a volume group

You first create a new physical volume on the block device you wish to use, then extend your volume group

    # pvcreate /dev/sdb1
    # vgextend VolGroup00 /dev/sdb1

This of course will increase the total number of physical extents on your volume group, which can be allocated by logical volumes as you see fit.

Note: It is considered good form to have a partition table on your storage medium below LVM. Use the appropriate type code: `8e` for MBR, and `8e00` for GPT partitions.

### Remove partition from a volume group

If you created a logical volume on the partition, remove it first.

All of the data on that partition needs to be moved to another partition. Fortunately, LVM makes this easy:

    # pvmove /dev/sdb1

If you want to have the data on a specific physical volume, specify that as the second argument to `pvmove`:

    # pvmove /dev/sdb1 /dev/sdf1

Then the physical volume needs to be removed from the volume group:

    # vgreduce myVg /dev/sdb1

Or remove all empty physical volumes:

    # vgreduce --all vg0

And lastly, if you want to use the partition for something else, and want to avoid LVM thinking that the partition is a physical volume:

    # pvremove /dev/sdb1

### Deactivate volume group

Just invoke

    # vgchange -a n my_volume_group

This will deactivate the volume group and allow you to unmount the container it is stored in.

## Logical volume types

This article or section needs expansion.

Reason: Add instructions for thin-provisioned volume creation and RAID volume creation. (Discuss in Talk:LVM#)

Besides simple logical volumes, LVM supports snapshots, logical volume caching, thin provisioned logical volumes and RAID.

### Snapshots

LVM allows you to take a snapshot of your system in a much more efficient way than a traditional backup. It does this efficiently by using a COW (copy-on-write) policy. The initial snapshot you take simply contains hard-links to the inodes of your actual data. So long as your data remains unchanged, the snapshot merely contains its inode pointers and not the data itself. Whenever you modify a file or directory that the snapshot points to, LVM automatically clones the data, the old copy referenced by the snapshot, and the new copy referenced by your active system. Thus, you can snapshot a system with 35GB of data using just 2GB of free space so long as you modify less than 2GB (on both the original and snapshot). In order to be able to create snapshots you need to have unallocated space in your volume group. Snapshot like any other volume will take up space in the volume group. So, if you plan to use snapshots for backing up your root partition do not allocate 100% of your volume group for root logical volume.

#### Configuration

You create snapshot logical volumes just like normal ones.

    # lvcreate --size 100M --snapshot --name snap01 /dev/mapper/vg0-pv

With that volume, you may modify less than 100M of data, before the snapshot volume fills up.

Reverting the modified 'pv' logical volume to the state when the 'snap01' snapshot was taken can be done with

    # lvconvert --merge /dev/vg0/snap01

In case the origin logical volume is active, merging will occur on the next reboot.(Merging can be done even from a LiveCD)

The snapshot will no longer exist after merging.

Also multiple snapshots can be taken and each one can be merged with the origin logical volume at will.

The snapshot can be mounted and backed up with dd or tar. The size of the backup file done with dd will be the size of the files residing on the snapshot volume. To restore just create a snapshot, mount it, and write or extract the backup to it. And then merge it with the origin.

This article or section needs expansion.

Reason: scripts to automate snapshots of root before updates, to rollback... updating `menu.lst` to boot snapshots (separate article?) (Discuss in Talk:LVM#)

Snapshots are primarily used to provide a frozen copy of a file system to make backups; a backup taking two hours provides a more consistent image of the file system than directly backing up the partition.

See Create root filesystem snapshots with LVM for automating the creation of clean root file system snapshots during system startup for backup and rollback.

dm-crypt/Encrypting an entire system#LVM on LUKS and dm-crypt/Encrypting an entire system#LUKS on LVM.

If you have LVM volumes not activated via the initramfs, enable `lvm-monitoring.service`, which is provided by the lvm2 package.

### LVM cache

From lvmcache(7):

  The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV. It does this by storing the frequently used blocks on the faster LV. LVM refers to the small fast LV as a cache pool LV. The large slow LV is called the origin LV. Due to requirements from dm-cache (the kernel driver), LVM further splits the cache pool LV into two devices - the cache data LV and cache metadata LV. The cache data LV is where copies of data blocks are kept from the origin LV to increase speed. The cache metadata LV holds the accounting information that specifies where data blocks are stored (e.g. on the origin LV or on the cache data LV). Users should be familiar with these LVs if they wish to create the best and most robust cached logical volumes. All of these associated LVs must be in the same VG.

#### Create cache

The fast method is creating a PV (if necessary) on the fast disk and add it to the existing volume group:

    # vgextend dataVG /dev/sdx

Create a cache pool with automatic meta data on sdb, and convert the existing logical volume (dataLV) to a cached volume, all in one step:

    # lvcreate --type cache --cachemode writethrough -L 20G -n dataLV_cachepool dataVG/dataLV /dev/sdx

Obviously, if you want your cache to be bigger, you can change the `-L` parameter to a different size.

Note: Cachemode has two possible options:

- `writethrough` ensures that any data written will be stored both in the cache pool LV and on the origin LV. The loss of a device associated with the cache pool LV in this case would not mean the loss of any data;
- `writeback` ensures better performance, but at the cost of a higher risk of data loss in case the drive used for cache fails.

If a specific `--cachemode` is not indicated, the system will assume `writethrough` as default.

#### Remove cache

If you ever need to undo the one step creation operation above:

    # lvconvert --uncache dataVG/dataLV

This commits any pending writes still in the cache back to the origin LV, then deletes the cache. Other options are available and described in lvmcache(7).

### RAID

From lvmraid(7):

  lvm(8) RAID is a way to create a Logical Volume (LV) that uses multiple physical devices to improve performance or tolerate device failures. In LVM, the physical devices are Physical Volumes (PVs) in a single Volume Group (VG).

LVM RAID supports RAID 0, RAID 1, RAID 4, RAID 5, RAID 6 and RAID 10. See Wikipedia:Standard RAID levels for details on each level.

#### Setup RAID

Create physical volumes:

    # pvcreate /dev/sda2 /dev/sdb2

Create volume group on the physical volumes:

    # vgcreate VolGroup00 /dev/sda2 /dev/sdb2

Create logical volumes useing `lvcreate --type raidlevel`, see lvmraid(7) and lvcreate(8) for more options.

    # lvcreate --type RaidLevel [OPTIONS] -n Name -L Size VG [PVs]

For example:

    # lvcreate --type raid1 --mirrors 1 -L 20G -n myraid1vol VolGroup00 /dev/sda2 /dev/sdb2

will create a 20GiB mirrored logical volume named "myraid1vol" in VolGroup00 on `/dev/sda2` and `/dev/sdb2`.

#### Configure mkinitcpio for RAID

If your root filesystem is on LVM RAID additionally to `lvm2` or `sd-lvm2` hooks, you need to add `dm-raid` and the appropriate RAID modules (e.g. `raid0`, `raid1`, `raid10` and/or `raid456`) to the MODULES array in `mkinitcpio.conf`.

For busybox based initramfs:

    /etc/mkinitcpio.conf

    MODULES=(dm-raid raid0 raid1 raid10 raid456)
    HOOKS=(base udev ... block lvm2 filesystems)

For systemd based initramfs:

    /etc/mkinitcpio.conf

    MODULES=(dm-raid raid0 raid1 raid10 raid456)
    HOOKS=(base systemd ... block sd-lvm2 filesystems)

## Graphical configuration

There is no "official" GUI tool for managing LVM volumes, but system-config-lvmAUR covers most of the common operations, and provides simple visualizations of volume state. It can automatically resize many file systems when resizing logical volumes.

## Troubleshooting

### Changes that could be required due to changes in the Arch-Linux defaults

The `use_lvmetad = 1` must be set in `/etc/lvm/lvm.conf`. This is the default now - if you have a `lvm.conf.pacnew` file, you must merge this change.

### LVM commands do not work

- Load proper module:

    # modprobe dm_mod

The `dm_mod` module should be automatically loaded. In case it does not, you can try:

The factual accuracy of this article or section is disputed.

Reason: Should module loading at boot be done using "/etc/modules-load.d" instead? (Discuss in Talk:LVM#)

    /etc/mkinitcpio.conf:

    MODULES=(dm_mod ...)

You will need to rebuild the initramfs to commit any changes you made.

- Try preceding commands with lvm like this:

    # lvm pvdisplay

### Logical Volumes do not show up

If you are trying to mount existing logical volumes, but they do not show up in `lvscan`, you can use the following commands to activate them:

    # vgscan
    # vgchange -ay

### LVM on removable media

Symptoms:

    # vgscan

      Reading all physical volumes.  This may take a while...
      /dev/backupdrive1/backup: read failed after 0 of 4096 at 319836585984: Input/output error
      /dev/backupdrive1/backup: read failed after 0 of 4096 at 319836643328: Input/output error
      /dev/backupdrive1/backup: read failed after 0 of 4096 at 0: Input/output error
      /dev/backupdrive1/backup: read failed after 0 of 4096 at 4096: Input/output error
      Found volume group "backupdrive1" using metadata type lvm2
      Found volume group "networkdrive" using metadata type lvm2

Cause:

  Removing an external LVM drive without deactivating the volume group(s) first. Before you disconnect, make sure to:

    # vgchange -an volume group name

Fix: assuming you already tried to activate the volume group with `# vgchange -ay vg`, and are receiving the Input/output errors:

    # vgchange -an volume group name

Unplug the external drive and wait a few minutes:

    # vgscan
    # vgchange -ay volume group name

### Resizing a contiguous logical volume fails

If trying to extend a logical volume errors with:

    " Insufficient suitable contiguous allocatable extents for logical volume "

The reason is that the logical volume was created with an explicit contiguous allocation policy (options `-C y` or `--alloc contiguous`) and no further adjacent contiguous extents are available (see also reference).

To fix this, prior to extending the logical volume, change its allocation policy with `lvchange --alloc inherit <logical_volume>`. If you need to keep the contiguous allocation policy, an alternative approach is to move the volume to a disk area with sufficient free extents (see [1]).

### Command "grub-mkconfig" reports "unknown filesystem" errors

Make sure to remove snapshot volumes before generating grub.cfg.

### Thinly-provisioned root volume device times out

With a large number of snapshots, `thin_check` runs for a long enough time so that waiting for the root device times out. To compensate, add the `rootdelay=60` kernel boot parameter to your boot loader configuration.

### Delay on shutdown

If you use RAID, snapshots or thin provisioning and experience a delay on shutdown, make sure `lvm2-monitor.service` is started. See FS#50420.

## See also

- LVM2 Resource Page on SourceWare.org
- LVM article at Gentoo wiki
- Ubuntu LVM Guide Part 1 Part 2 detals snapshots
- Red Hat: Logical Volume Manager Administration

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- File systems

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