Difference between revisions of "LVM"
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Revision as of 08:36, 26 November 2018
- LVM is a logical volume manager for the Linux kernel; it manages disk drives and similar mass-storage devices.
- 1 LVM Building Blocks
- 2 Advantages
- 3 Disadvantages
- 4 Installing Arch Linux on LVM
- 5 Volume operations
- 5.1 Advanced options
- 5.2 Resizing volumes
- 5.3 Renaming volumes
- 5.4 Remove logical volume
- 5.5 Add physical volume to a volume group
- 5.6 Remove partition from a volume group
- 5.7 Deactivate volume group
- 6 Logical volume types
- 7 Graphical configuration
- 8 Troubleshooting
- 8.1 Boot/Shutdown-problems because of disabled lvmetad
- 8.2 LVM commands do not work
- 8.3 Logical Volumes do not show up
- 8.4 LVM on removable media
- 8.5 Resizing a contiguous logical volume fails
- 8.6 Command "grub-mkconfig" reports "unknown filesystem" errors
- 8.7 Thinly-provisioned root volume device times out
- 8.8 Delay on shutdown
- 9 See also
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.
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 | |_ _ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|
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
/backup, etc.) without the hassle of entering a key multiple times on boot.
- 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 installed.package is
- 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
/etc/mkinitcpio.conf(see below for details).
/bootcannot reside in LVM when using a boot loader which does not support LVM; you must create a separate
/bootpartition and format it directly. Only GRUB is known to support LVM.
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
Linux LVMin fdisk).
- If you use GUID Partition Table, set the partition type GUID to
Linux LVMin fdisk and
Create physical volumes
To list all your devices capable of being used as a physical volume:
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:
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>
Seefor a list of valid characters for volume group names.
# 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> # ...
# vgextend VolGroup00 /dev/sdb1 # vgextend VolGroup00 /dev/sdc
You can track how your volume group grows with:
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
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>
# 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 .
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:
modprobe dm_mod') for the above commands to succeed.
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>
# mkfs.ext4 /dev/VolGroup00/lvolhome # mount /dev/VolGroup00/lvolhome /home
/dev/Volgroup00/lvolhome). Do not select the actual partitions on which logical volumes were created (do not use:
In case your root filesystem is on LVM, you will need to enable the appropriate mkinitcpio hooks, otherwise your system might not boot. Enable:
lvm2for the default busybox based initramfs
sd-lvm2for systemd based initramfs
udev is there by default. Edit the file and insert
filesystems like so:
HOOKS=(base udev ... block lvm2 filesystems)
For systemd based initramfs:
HOOKS=(base systemd ... block sd-lvm2 filesystems)
Afterwards, you can continue in normal installation instructions with the create an initial ramdisk step.
sd-lvm2hooks are installed by , not . If you are running mkinitcpio in an arch-chroot for a new installation, must be installed inside the arch-chroot for mkinitcpio to find the
sd-lvm2hook. If 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.
If the root file system resides in a logical volume, the
root= kernel parameter must be pointed to the mapped device, e.g
You can restrict the volumes that are activated automatically by setting the
/etc/lvm/lvm.conf. If in doubt, leave this option commented out.
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
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.
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
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
# 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/sdd1:0-92467
/dev/sdd1: Moved: 0.1 % /dev/sdd1: Moved: 0.2 % ... /dev/sdd1: Moved: 99.9 % /dev/sdd1: Moved: 100.0 %
- this command moves 399668 - 307201 + 1 = 92468 PEs from the last segment to the first segment. This is possible as the first segment encloses 153600 free PEs, which can contain the 92467 - 0 + 1 = 92468 moved PEs.
--alloc anywhereoption 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:
PV VG Fmt Attr PSize PFree /dev/sdd1 vg1 lvm2 a-- 1t 500g
Last, you need to shrink the partition with your favorite partitioning tool.
--resizefsoption which allows to resize the file system together with the LV using (ext2, ext3, ext4, ReiserFS and XFS supported). Therefore it may be easier to simply use
lvresizefor both operations and use
--resizefsto simplify things a bit, except if you have specific needs or want full control over the process.
Resizing the logical volume and file system in one go
Extend the logical volume
MyVolGroup by 10 GiB and resize its file system all at once:
# lvresize -L +10G --resizefs MyVolGroup/mediavol
Set the size of logical volume
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
Seefor more detailed options.
Resizing the logical volume and file system separately
For file systems not supported by appropriate utility to resize the file system before shrinking the logical volume or after expanding it.will need to use the
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
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
Seefor more detailed options.
Renaming a Volume Group
Use thecommand to rename an existing volume group.
Either of the following commands renames the existing volume group
# vgrename /dev/vg02 /dev/my_volume_group
# vgrename vg02 my_volume_group
Renaming Logical Volumes
To rename an existing logical volume, use thecommand.
Either of the following commands renames logical volume
lvold in volume group
# lvrename /dev/vg02/lvold /dev/vg02/lvnew
# lvrename vg02 lvold lvnew
Remove logical volume
First, find out the name of the logical volume you want to remove. You can get a list of all logical volumes with:
Next, look up the mountpoint of the chosen logical volume:
Then unmount the filesystem on the logical volume:
# umount /<mountpoint>
Finally, remove the logical volume:
# lvremove <volume_group>/<logical_volume>
# lvremove VolGroup00/lvolhome
Confirm by typing in
/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.
8efor MBR, and
8e00for 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 /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
# 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
Besides simple logical volumes, LVM supports snapshots, logical volume caching, thin provisioned logical volumes and RAID.
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.
You create snapshot logical volumes just like normal ones.
# lvcreate --size 100M --snapshot --name snap01 /dev/vg0/lv
With that volume, you may modify less than 100 MiB of data, before the snapshot volume fills up.
Reverting the modified 'lv' 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).
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.
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.
- 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.
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.
writethroughensures 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;
writebackensures 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.
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.
- 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.
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 and for more options.
# lvcreate --type RaidLevel [OPTIONS] -n Name -L Size VG [PVs]
# 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
Configure mkinitcpio for RAID
If your root filesystem is on LVM RAID additionally to
sd-lvm2 hooks, you need to add
dm-raid and the appropriate RAID modules (e.g.
raid456) to the MODULES array in
For busybox based initramfs:
MODULES=(dm-raid raid0 raid1 raid10 raid456) HOOKS=(base udev ... block lvm2 filesystems)
For systemd based initramfs:
MODULES=(dm-raid raid0 raid1 raid10 raid456) HOOKS=(base systemd ... block sd-lvm2 filesystems)
There is no "official" GUI tool for managing LVM volumes, butAUR covers most of the common operations, and provides simple visualizations of volume state. It can automatically resize many file systems when resizing logical volumes.
Boot/Shutdown-problems because of disabled lvmetad
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
dm_mod module should be automatically loaded. In case it does not, you can try:
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
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
- 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 ).
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.