Difference between revisions of "LVM"

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You should create your LVM Volumes between the [[partitioning]] and [[File systems#Create a file system|formatting]] steps of the [[Installation guide|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).  
 
You should create your LVM Volumes between the [[partitioning]] and [[File systems#Create a file system|formatting]] steps of the [[Installation guide|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 {{pkg|lvm2}} package is [[installed]].
+
Make sure the {{pkg|lvm2}} package is [[install]]ed.
  
 
Quick overview:  
 
Quick overview:  

Revision as of 06:40, 30 September 2018

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 4 MiB). Think of physical extents as parts of disks that can be allocated to any partition.

Example:

Physical disks
                
  Disk1 (/dev/sda):
     _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    |Partition1 50 GiB (Physical volume) |Partition2 80 GiB (Physical volume)     |
    |/dev/sda1                           |/dev/sda2                               |
    |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |
                                  
  Disk2 (/dev/sdb):
     _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    |Partition1 120 GiB (Physical volume)                 |
    |/dev/sdb1                                            |
    |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|
LVM logical volumes

  Volume Group1 (/dev/MyVolGroup/ = /dev/sda1 + /dev/sda2 + /dev/sdb1):
     _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    |Logical volume1 15 GiB  |Logical volume2 35 GiB      |Logical volume3 200 GiB              |
    |/dev/MyVolGroup/rootvol |/dev/MyVolGroup/homevol     |/dev/MyVolGroup/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 (e.g. 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.
  • 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

Partition the device as required before configuring LVM.

Create the partitions:

  • If you use Master Boot Record partition table, set the partition type ID to 8e (partition type Linux LVM in fdisk).
  • If you use GUID Partition Table, set the partition type GUID to E6D6D379-F507-44C2-A23C-238F2A3DF928 (partition type Linux LVM in fdisk and 8e00 in gdisk).

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 < 1 MiB), 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>

See lvm(8) for a list of valid characters for volume group names.

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/VolGroup00/lvolhome. Just like volume groups, you can use any name you want for your logical volume when creating it besides a few exceptions listed in lvm(8).

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/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/<volume_group>/<logical_volume>
# mount /dev/<volume_group>/<logical_volume> /<mountpoint>

For example:

# mkfs.ext4 /dev/VolGroup00/lvolhome
# mount /dev/VolGroup00/lvolhome /home
Warning: When choosing mountpoints, just select your newly created logical volumes (use: /dev/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/vg-name/lv-name.

Volume operations

Advanced options

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(8) provides more or less the same options as the specialized lvextend(8) and lvreduce(8) 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.
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.
Resizing the logical volume and file system in one go
Note: Only ext2, ext3, ext4, ReiserFS and XFS file systems are supported. For a different type of file system see #Resizing the logical volume and file system separately.

Extend the logical volume mediavol in MyVolGroup by 10 GiB and resize its file system all at once:

# lvresize -L +10G --resizefs MyVolGroup/mediavol

Set the size of logical volume mediavol in MyVolGroup to 15 GiB and resize its file system all at once:

# lvresize -L 15G --resizefs MyVolGroup/mediavol

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

# lvresize -l +100%FREE --resizefs MyVolGroup/mediavol

See lvresize(8) for more detailed options.

Resizing the logical volume and file system separately

For file systems not supported by fsadm(8) will need to use the appropriate utility to resize the file system before shrinking the logical volume or after expanding it.

To extend logical volume mediavol within volume group MyVolGroup by 2 GiB without touching its file system:

# lvresize -L +2G MyVolGroup/mediavol

Now expand the file system (ext4 in this example) to the maximum size of the underlying logical volume:

# resize2fs /dev/MyVolGroup/mediavol

To reduce the size of logical volume mediavol in MyVolGroup by 500 MiB, first calculate the resulting file system size and shrink the file system (ext4 in this example) to the new size:

# resize2fs /dev/MyVolGroup/mediavol NewSize

When the file system is shrunk, reduce the size of logical volume:

# lvresize -L -500M MyVolGroup/mediavol

See lvresize(8) for more detailed options.

Renaming volumes

Renaming a Volume Group

Use the vgrename(8) command to rename an existing volume group.

Either of the following commands renames the existing volume group vg02 to my_volume_group

# vgrename /dev/vg02 /dev/my_volume_group
# vgrename vg02 my_volume_group

Renaming Logical Volumes

To rename an existing logical volume, use the lvrename(8) command.

Either of the following commands renames logical volume lvold in volume group vg02 to lvnew.

# lvrename /dev/vg02/lvold /dev/vg02/lvnew
# lvrename vg02 lvold lvnew

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

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

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

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 35 GiB of data using just 2 GiB of free space so long as you modify less than 2 GiB (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/vg0/pv

With that volume, you may modify less than 100 MiB 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).

Note: 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.

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

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 20 GiB 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

Boot/Shutdown-problems because of disabled lvmetad

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:

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

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 regenerate 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