Logical Volume Manager
LVM is a disk management tool, which is a device mapper for linux kernel,managing storage systems than the traditional partition based one.In LVM instead of creating partitions you create
logical volumes, /boot cannot use logical volumes.
LVM offers features like striping,mirroring,snapshotting.LVM functions by layering abstractions on top of physical storage devices.
Main components of LVM are
Physical Volumes: physical block devices which are set a hard disks,physical volumes are regular storage devices,prefixed withpv..Volume Groups: LVM combines physical volumes into storage pools known as volume groups,LVM abstracts the function there by making a unified logical devices with one ,prefixed withvg...Logical Volumes: a volume group is sliced into a number of logical volumes.Logical volumes are functionally equivalent to partitions on a physical disks,but with more advanced features.
Basic LVM Commands
Making Physical Devices as Physical Volumes.
- lvmdiskscan - returns the number of block devices to which LVM can interact.
vinay@kevin ~> sudo lvmdiskscan
/dev/sda [ 57.30 GiB]
/dev/nvme0n1p1 [ <464.81 GiB]
/dev/nvme0n1p5 [ 975.00 MiB]
/dev/sdb [ <28.87 GiB]
2 disks
2 partitions
0 LVM physical volume whole disks
0 LVM physical volumesHere we are creating a physical volume for the disks /dev/sda and /dev/sdb.
- pvcreate - command that is used to initialize physical disks to physical volumes for LVM, this will write an LVM header to the devices to indicate that they are ready to be added to volume group.
vinay@kevin ~> sudo pvcreate /dev/sda /dev/sdb
Physical volume "/dev/sda" successfully created.
Physical volume "/dev/sdb" successfully created.- pvs - displays information about physical volumes.
vinay@kevin ~> sudo pvs
PV VG Fmt Attr PSize PFree
/dev/sda lvm2 --- 57.30g 57.30g
/dev/sdb lvm2 --- <28.87g <28.87gthe disks /dev/sda and /dev/sdb is of the size 57G and 28G respectively,hence these can be added to the volume groups.
Add Physical Volumes to Volume Group.
- vgcreate - creates a volume group
vinay@kevin ~> sudo vgcreate VolGrpLvm /dev/sda /dev/sdb
Volume group "VolGrpLvm" successfully createda volume group with the name, VolGrpLvm is created
- vgs - displays information about volume groups
vinay@kevin ~> sudo vgs
VG #PV #LV #SN Attr VSize VFree
VolGrpLvm 2 0 0 wz--n- 86.16g 86.16gHere the two phyical volumes are converted into a pool of storage,making a total of 86G, from this pool of storage,these are sliced to several logical volumes.
Creating Logical Volumes from the Volume Group Pool.
- lvcreate - creating a logical volume from the volume group
vinay@kevin ~> sudo lvcreate -L 10G -n backup VolGrpLvm
Logical volume "backup" created.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-a----- 10.00glvcreate is used to create a logical volume from the volume group of storage pool, -L option is used to specify the size of the volume and -n option is used to label the logical volume.
lvs displays information about the logical volume created.
Similarly create another logical volume.
vinay@kevin ~> sudo lvcreate -L 30G -n college-data VolGrpLvm
Logical volume "college-data" created.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-a----- 10.00g
college-data VolGrpLvm -wi-a----- 30.00g Format and Mount the logical volumes
Formatting the logical volumes.
$ sudo mkfs.ext4 /dev/VolGrpLvm/backup
$ sudo mkfs.ext4 /dev/VolGrpLvm/college-dataMounting the logical volume
vinay@kevin ~> sudo mkdir -p /mnt/{backup,college-data}
vinay@kevin ~> sudo mount /dev/VolGrpLvm/backup /mnt/backup/
vinay@kevin ~> sudo mount /dev/VolGrpLvm/college-data /mnt/college-data/
vinay@kevin ~> lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 1 57.3G 0 disk
├─VolGrpLvm-backup 254:0 0 10G 0 lvm /mnt/backup
└─VolGrpLvm-college--data 254:1 0 30G 0 lvm /mnt/college-data
sdb 8:16 1 28.9G 0 disk
nvme0n1 259:0 0 465.8G 0 disk
├─nvme0n1p1 259:1 0 464.8G 0 part /
├─nvme0n1p2 259:2 0 1K 0 part
└─nvme0n1p5 259:3 0 975M 0 part [SWAP]Creating mount points in /mnt and mount the volumes onto the mountpoints created.
Other useful scan and display commands.
vinay@kevin ~> sudo pvscan
PV /dev/sda VG VolGrpLvm lvm2 [57.30 GiB / 17.30 GiB free]
PV /dev/sdb VG VolGrpLvm lvm2 [28.86 GiB / 28.86 GiB free]
Total: 2 [86.16 GiB] / in use: 2 [86.16 GiB] / in no VG: 0 [0 ]
vinay@kevin ~> sudo lvscan
ACTIVE '/dev/VolGrpLvm/backup' [10.00 GiB] inherit
ACTIVE '/dev/VolGrpLvm/college-data' [30.00 GiB] inherit
vinay@kevin ~> sudo vgscan
Found volume group "VolGrpLvm" using metadata type lvm2
vinay@kevin ~> s^C
vinay@kevin ~>
vinay@kevin ~> sudo pvscan
PV /dev/sda VG VolGrpLvm lvm2 [57.30 GiB / 17.30 GiB free]
PV /dev/sdb VG VolGrpLvm lvm2 [28.86 GiB / 28.86 GiB free]
Total: 2 [86.16 GiB] / in use: 2 [86.16 GiB] / in no VG: 0 [0 ]
vinay@kevin ~> sudo vgscan
Found volume group "VolGrpLvm" using metadata type lvm2
vinay@kevin ~> sudo lvscan
ACTIVE '/dev/VolGrpLvm/backup' [10.00 GiB] inherit
ACTIVE '/dev/VolGrpLvm/college-data' [30.00 GiB] inherit
vinay@kevin ~> sudo pvdisplay
--- Physical volume ---
PV Name /dev/sda
VG Name VolGrpLvm
PV Size 57.30 GiB / not usable 4.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 14669
Free PE 4429
Allocated PE 10240
PV UUID obDX3S-49P0-0Y2o-Vpr1-zFxV-Tgng-Ov9oEz
— Physical volume —
PV Name /dev/sdb
VG Name VolGrpLvm
PV Size <28.87 GiB / not usable 4.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 7389
Free PE 7389
Allocated PE 0
PV UUID 7KAaVc-1H9V-FSsK-n98X-P9SM-IIAw-s9Myce
vinay@kevin ~> sudo vgdisplay
— Volume group —
VG Name VolGrpLvm
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 2
Max PV 0
Cur PV 2
Act PV 2
VG Size 86.16 GiB
PE Size 4.00 MiB
Total PE 22058
Alloc PE / Size 10240 / 40.00 GiB
Free PE / Size 11818 / 46.16 GiB
VG UUID P1dIv1-Lk34-Oxjo-ZZoE-81ys-3XnL-5WZotd
vinay@kevin ~> sudo lvdisplay
— Logical volume —
LV Path /dev/VolGrpLvm/backup
LV Name backup
VG Name VolGrpLvm
LV UUID CjtnRq-evig-hsY4-avOM-6KVM-a7TT-VeAkDR
LV Write Access read/write
LV Creation host, time kevin, 2024-01-03 10:41:55 +0530
LV Status available
open 1
LV Size 10.00 GiB
Current LE 2560
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 254:0
— Logical volume —
LV Path /dev/VolGrpLvm/college-data
LV Name college-data
VG Name VolGrpLvm
LV UUID f2zixQ-ayec-zrXb-AV35-JaU0-9jz5-9ZrFtk
LV Write Access read/write
LV Creation host, time kevin, 2024-01-03 10:45:39 +0530
LV Status available
open 1
LV Size 30.00 GiB
Current LE 7680
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 254:1
Rename a LV
Renaming a logical volume using lvrename
vinay@kevin ~> sudo lvrename /dev/VolGrpLvm/college-data /dev/VolGrpLvm/college
Renamed "college-data" to "college" in volume group "VolGrpLvm"
vinay@kevin ~> ls /dev/VolGrpLvm/
backup@ college@Extending a LV
To increase the size of the logical volume,we use lvextend command.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-ao---- 10.00g
college VolGrpLvm -wi-ao---- 30.00g
vinay@kevin ~> sudo lvextend -L+5G /dev/VolGrpLvm/backup
Size of logical volume VolGrpLvm/backup changed from 10.00 GiB (2560 extents) to 15.00 GiB (3840 extents).
Logical volume VolGrpLvm/backup successfully resized.To increase the size of the volume by specified size use the + character to mention the increase in size.
To set the size of the volume see the below example.
vinay@kevin ~> sudo lvextend -L25G /dev/VolGrpLvm/backup
Size of logical volume VolGrpLvm/backup changed from 15.00 GiB (3840 extents) to 25.00 GiB (6400 extents).
Logical volume VolGrpLvm/backup successfully resized.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-ao---- 25.00g
college VolGrpLvm -wi-ao---- 30.00gShrink a LV
Can reduce the size of the volume using lvreduce command.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-ao---- 25.00g
college VolGrpLvm -wi-ao---- 30.00g
vinay@kevin ~> sudo lvreduce -L20G /dev/VolGrpLvm/backup
WARNING: Reducing active and open logical volume to 20.00 GiB.
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce VolGrpLvm/backup? [y/n]: y
Size of logical volume VolGrpLvm/backup changed from 25.00 GiB (6400 extents) to 20.00 GiB (5120 extents).
Logical volume VolGrpLvm/backup successfully resized.
vinay@kevin ~> sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
backup VolGrpLvm -wi-ao---- 20.00g
college VolGrpLvm -wi-ao---- 30.00gHere,the size of the volume is reduced to 20G.
Remove an LV
Before removing an LV,umount it first and then use the lvremove to remove the volume group.
vinay@kevin ~> sudo lvremove /dev/VolGrpLvm/backup
Do you really want to remove active logical volume VolGrpLvm/backup? [y/n]: y
Logical volume "backup" successfully removed.Increase Pool storage
To increase the size of the volume group we use the command vgextend to increase the size of the storage pool.
Initially the size of the volume storage pool was 86G and now it is increased to 115G
/dev/sdc is the new phyical volume.
vinay@kevin ~> sudo pvcreate /dev/sdc
Physical volume "/dev/sdc" successfully created.
vinay@kevin ~> sudo vgs
VG #PV #LV #SN Attr VSize VFree
VolGrpLvm 2 1 0 wz--n- 86.16g 56.16g
vinay@kevin ~> sudo vgextend VolGrpLvm /dev/sdc
Volume group "VolGrpLvm" successfully extended
vinay@kevin ~> sudo vgs
VG #PV #LV #SN Attr VSize VFree
VolGrpLvm 3 1 0 wz--n- <115.03g <85.03gStriping
RAID 0: Striping
RAID 0,also known as striped set or striped volume,requires a minimum of two disks, the disks are merged into one single large volume and data is stored evenly the disks.This process is called disk striping and involves splitting data into blocks and writing it simultaneously/sequentially on multiple disks. It doesn’t support redundancy,fault tolerance and hence data loss.
Data is stored sequentially
vinay@kevin ~> sudo lvcreate -L 10G -i2 -I64 -n backup1 VolGrpLvm
[sudo] password for vinay:
WARNING: ext4 signature detected on /dev/VolGrpLvm/backup1 at offset 1080. Wipe it? [y/n]: y
Wiping ext4 signature on /dev/VolGrpLvm/backup1.
Logical volume "backup1" created.Creating a logical volume with the size 10G, the -i argument is used to mention striping and the number next to the option specifies the striping in how many disks, the -I option in the above command is to specify the size of block of 64kB across two physical volumes.
If the striping number across the disks is more than the physical volumes,it fails to create a logical volume,with an exeception saying number of stripes exceeds number of physical volumes.
vinay@kevin ~> sudo lvcreate -L 5G -i4 -I64 -n backup3 VolGrpLvm
Number of stripes (4) must not exceed number of physical volumes (3)In this setup only 3 physical volumes are used,which exceeds the stripe number.
Mirroring
RAID 1: Disk Mirroring Keeping a copy of the data within the logical volume is called mirroring,for redundancy and to avoid data loss.
the -m option with value 1 creates one copy of the data,therefore having a total of two copies of data within the file system,-m2 creates two mirrors,yielding three copies of the file system.
vinay@kevin ~> sudo lvcreate -L 5G -m1 -n mirrorLV VolGrpLvm
Logical volume "mirrorLV" created.Thin Volumes
Usually LVM normally allocates blocks when you create a volume,thats thick provisioning.LVM thin pools instead allocates blocks when they are written,this is called thin provisioning. Because volumes can be much larger than physically available space.
- To remove a physical volume from the existing volume group,use vgreduce
vinay@kevin ~ [5]> sudo vgreduce VolGrpLvm /dev/sdc
Removed "/dev/sdc" from volume group "VolGrpLvm"Create new physical volumes using physical disks and create a volume group.
vinay@kevin ~> sudo pvcreate /dev/sdc /dev/sdd
Physical volume "/dev/sdc" successfully created.
Physical volume "/dev/sdd" successfully created.
vinay@kevin ~> sudo vgcreate vg_thin /dev/sdc /dev/sdd
Volume group "vg_thin" successfully createdCreate a thinpool with the size 5G with chunksize 256K where ```vg_thin`` is the volume group name and creating a pool again within the volume group
vinay@kevin ~> sudo lvcreate --thin --size 5G --chunksize 256K --poolmetadatasize 1G vg_thin/thin_pool
Thin pool volume with chunk size 256.00 KiB can address at most 63.50 TiB of data.
Logical volume "thin_pool" created.Listing all the logical volumes which displays all the logical volumes
vinay@kevin ~> sudo lvs -a
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
[lvol0_pmspare] vg_thin ewi------- 1.00g
thin_pool vg_thin twi-a-tz-- 5.00g 0.00 1.57
[thin_pool_tdata] vg_thin Twi-ao---- 5.00g
[thin_pool_tmeta] vg_thin ewi-ao---- 1.00g Creating 3 logical volumes,while for the second logical volujme volume_2 there is a warning which mentions exceeds the size of thin pool,even though the pool size is 5G,after the creation of the first logical volume volume_1 2G should be remained,since it is thin provisioning, only when data is written blocks are allocated to it,so hence just a warning.
Similarly the error comes during the creation of volume_3.
vinay@kevin ~> sudo lvcreate --thinpool vg_thin/thin_pool --name volume_1 --virtualsize 3G
Logical volume "volume_1" created.
vinay@kevin ~> sudo lvcreate --thinpool vg_thin/thin_pool --name volume_2 --virtualsize 3G
WARNING: Sum of all thin volume sizes (6.00 GiB) exceeds the size of thin pool vg_thin/thin_pool (5.00 GiB).
WARNING: You have not turned on protection against thin pools running out of space.
WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
Logical volume "volume_2" created.
vinay@kevin ~> sudo lvcreate --thinpool vg_thin/thin_pool --name volume_3 --virtualsize 3G
WARNING: Sum of all thin volume sizes (9.00 GiB) exceeds the size of thin pool vg_thin/thin_pool (5.00 GiB).
WARNING: You have not turned on protection against thin pools running out of space.
WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
Logical volume "volume_3" created.All the logical volumes can be verfied now.
vinay@kevin ~> sudo lvs -a
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
[lvol0_pmspare] vg_thin ewi------- 1.00g
thin_pool vg_thin twi-aotz-- 5.00g 0.00 1.57
[thin_pool_tdata] vg_thin Twi-ao---- 5.00g
[thin_pool_tmeta] vg_thin ewi-ao---- 1.00g
volume_1 vg_thin Vwi-a-tz-- 3.00g thin_pool 0.00
volume_2 vg_thin Vwi-a-tz-- 3.00g thin_pool 0.00
volume_3 vg_thin Vwi-a-tz-- 3.00g thin_pool 0.00