Henzel Moras
April 18, 2021
Logical Volume Manager
About Logical Volume Manager
One or more physical volumes (disk partitions) are grouped together into a volume group. Then, the volume group is subdivided into logical volumes, which mimic to the system nominal physical disk partitions and can be formatted to contain mountable filesystems.
Logical volumes are created by putting all the devices into a large pool of disk space (the volume group), and then allocating space from the pool to create a logical volume.
LVM has better scalability than RAID: logical volumes can easily be resized; i.e., enlarged or shrunk, as needs require. If more space is needed, additional devices can be added to the logical volume at any time.
LVM Components
There are a number of command line utilities used to create and manipulate volume groups, whose name always start with vg, including:
- vgcreate: Creates volume groups.
- vgextend: Adds to volume groups.
- vgreduce: Shrinks volume groups.
Utilities that manipulate what physical partitions enter or leave volume groups start with pv and include:
- pvcreate: Converts a partition to a physical volume.
- pvdisplay: Shows the physical volumes being used.
- pvmove: Moves the data from one physical volume within the volume group to others; this might be required if a disk or partition is being removed for some reason. It would then be followed by:
- pvremove: Remove a partition from a physical volume.
Typing man lvm will give a full list of LVM utilities.
or
check /sbin/
/sbin/pv*
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo ls -lf /sbin/pv*
/sbin/pvchange /sbin/pvcreate /sbin/pvmove /sbin/pvresize /sbin/pvscan
/sbin/pvck /sbin/pvdisplay /sbin/pvremove /sbin/pvs
/sbin/vg*
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo ls -lf /sbin/vg*
/sbin/vgcfgbackup /sbin/vgcreate /sbin/vgimportclone /sbin/vgrename
/sbin/vgcfgrestore /sbin/vgdisplay /sbin/vgmerge /sbin/vgs
/sbin/vgchange /sbin/vgexport /sbin/vgmknodes /sbin/vgscan
/sbin/vgck /sbin/vgextend /sbin/vgreduce /sbin/vgsplit
/sbin/vgconvert /sbin/vgimport /sbin/vgremove
/sbin/lv*
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo ls -lf /sbin/lv*
/sbin/lvchange /sbin/lvm /sbin/lvmsadc /sbin/lvresize
/sbin/lvconvert /sbin/lvmconfig /sbin/lvmsar /sbin/lvs
/sbin/lvcreate /sbin/lvmdiskscan /sbin/lvreduce /sbin/lvscan
/sbin/lvdisplay /sbin/lvmdump /sbin/lvremove
/sbin/lvextend /sbin/lvmpolld /sbin/lvrename
Create LVM
lets make use of /dev/sdb partitions
[s0x45ker--_(+_+)_--SysAdmin ~]$ lsblk /dev/sdb
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:16 0 2G 0 disk
├─sdb1 8:17 0 256M 0 part
├─sdb2 8:18 0 256M 0 part
└─sdb3 8:19 0 1.5G 0 part
Create Physical Volumes
lets create pv groups
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo pvcreate /dev/sdb1
WARNING: ext4 signature detected on /dev/sdb1 at offset 1080. Wipe it? [y/n]: y
Wiping ext4 signature on /dev/sdb1.
Physical volume "/dev/sdb1" successfully created.
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo pvcreate /dev/sdb2
WARNING: ext4 signature detected on /dev/sdb2 at offset 1080. Wipe it? [y/n]: y
Wiping ext4 signature on /dev/sdb2.
Physical volume "/dev/sdb2" successfully created.
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo pvcreate /dev/sdb3
WARNING: ext4 signature detected on /dev/sdb3 at offset 1080. Wipe it? [y/n]: y
Wiping ext4 signature on /dev/sdb3.
Physical volume "/dev/sdb3" successfully created.
Display PV
lets display them
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo pvdisplay
--- Physical volume ---
PV Name /dev/sda2
VG Name cl
PV Size <20.32 GiB / not usable 0
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 5201
Free PE 0
Allocated PE 5201
PV UUID HkaGdc-0SM4-q58B-GLpF-yBKh-dluM-Zb7psU
"/dev/sdb1" is a new physical volume of "256.00 MiB"
--- NEW Physical volume ---
PV Name /dev/sdb1
VG Name
PV Size 256.00 MiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID r4DxPp-DwXw-MTKV-0rgJ-wslR-WvXf-ddTp95
"/dev/sdb2" is a new physical volume of "256.00 MiB"
--- NEW Physical volume ---
PV Name /dev/sdb2
VG Name
PV Size 256.00 MiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID p1MmuS-FtMY-TSfc-QTs0-f5kQ-8H02-G2hAkM
"/dev/sdb3" is a new physical volume of "<1.50 GiB"
--- NEW Physical volume ---
PV Name /dev/sdb3
VG Name
PV Size <1.50 GiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID Sg0adM-I34I-WdtH-FSBh-fv4E-6v0q-MfwpBh
Create Volume Groups
lets create vg groups
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo vgcreate myvgName /dev/sdb1 /dev/sdb2
Volume group "myvgName" successfully created
Display Volume Groups
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo vgdisplay
--- Volume group ---
VG Name myvgName
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 2
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 0
Max PV 0
Cur PV 2
Act PV 2
VG Size 504.00 MiB
PE Size 4.00 MiB
Total PE 126
Alloc PE / Size 125 / 500.00 MiB
Free PE / Size 1 / 4.00 MiB
VG UUID 22zcce-qKWO-LsZ4-NsIK-2LaG-BihC-PXpOu3
--- Volume group ---
VG Name cl
System ID
Format lvm2
Metadata Areas 1
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 1
Act PV 1
VG Size <20.32 GiB
PE Size 4.00 MiB
Total PE 5201
Alloc PE / Size 5201 / <20.32 GiB
Free PE / Size 0 / 0
VG UUID KE3I02-N1rq-Jt6O-EfGT-jFFc-thKG-Bu7w0V
Create Logical Volumes
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvcreate -L 500M -n mylvmName myvgName
Logical volume "mylvmName" created.
Display Logical Volumes
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvdisplay
--- Logical volume ---
LV Path /dev/myvgName/mylvmName
LV Name mylvmName
VG Name myvgName
LV UUID O3Tq2d-Ncn6-Ek56-ZJv5-l6pg-Cf25-4dcc4D
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2021-04-17 12:50:40 +0530
LV Status available
# open 0
LV Size 500.00 MiB
Current LE 125
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:2
--- Logical volume ---
LV Path /dev/cl/swap
LV Name swap
VG Name cl
LV UUID U40evz-UBNH-NuhE-6vn9-yW96-cC2B-1xgZgW
LV Write Access read/write
LV Creation host, time localhost, 2020-11-12 19:37:26 +0530
LV Status available
# open 2
LV Size <2.07 GiB
Current LE 529
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:1
--- Logical volume ---
LV Path /dev/cl/root
LV Name root
VG Name cl
LV UUID pfO1zZ-tB1E-a0p1-SCa9-68nu-jwMc-vK316T
LV Write Access read/write
LV Creation host, time localhost, 2020-11-12 19:37:26 +0530
LV Status available
# open 1
LV Size 18.25 GiB
Current LE 4672
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
Put A Filesystem on LVM
using mkfs
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo mkfs.ext4 /dev/myvgName/mylvmName
mke2fs 1.45.6 (20-Mar-2020)
Creating filesystem with 512000 1k blocks and 128016 inodes
Filesystem UUID: b8106acd-3151-408b-9c73-e2d1fdf8191e
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
Allocating group tables: done
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
Create Dir for Mount
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo mkdir /mylvmpnt
Mount Filesystem
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo mount /dev/myvgName/mylvmName /mylvmpnt
Check Filesystem mount
[s0x45ker--_(+_+)_--SysAdmin ~]$ df -Th | grep lvm
/dev/mapper/myvgName-mylvmName ext4 477M 2.3M 445M 1% /mylvmpnt
Make persistent Mount
using fstab
[s0x45ker--*(+*+)_--SysAdmin ~]$ sudo nano /etc/fstab
#
# /etc/fstab
# Created by anaconda on Thu Nov 12 19:37:28 2020
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
#
# After editing this file, run 'systemctl daemon-reload' to update systemd
# units generated from this file.
#
/dev/mapper/cl-root / xfs defaults 0 0
UUID=03f520f5-2aec-411c-a15b-3e2f62ffc37c /boot ext4 defaults 1 2
/dev/mapper/cl-swap swap swap defaults 0 0
/dev/myvgName/mylvmName /mylvmpnt ext4 defaults 0 0
Extent LVM
using lvresize
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvresize -r -L +200M /dev/myvgName/mylvmName
Insufficient free space: 50 extents needed, but only 1 available
Extend Volume Group
lets resize Volume Group
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo vgextend myvgName /dev/sdb3
Volume group "myvgName" successfully extended
display extended vg
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo vgdisplay myvgName
--- Volume group ---
VG Name myvgName
System ID
Format lvm2
Metadata Areas 3
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 3
Act PV 3
VG Size <1.99 GiB
PE Size 4.00 MiB
Total PE 509
Alloc PE / Size 125 / 500.00 MiB
Free PE / Size 384 / 1.50 GiB
VG UUID 22zcce-qKWO-LsZ4-NsIK-2LaG-BihC-PXpOu3
Finally lets our LVM
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvresize -r -L +200M /dev/myvgName/mylvmName
Size of logical volume myvgName/mylvmName changed from 500.00 MiB (125 extents) to 700.00 MiB (175 extents).
Logical volume myvgName/mylvmName successfully resized.
resize2fs 1.45.6 (20-Mar-2020)
Filesystem at /dev/mapper/myvgName-mylvmName is mounted on /mylvmpnt; on-line resizing required
old_desc_blocks = 4, new_desc_blocks = 6
The filesystem on /dev/mapper/myvgName-mylvmName is now 716800 (1k) blocks long.
Create LVM Snapshot
LVM snapshots create an exact copy of an existing logical volume. They are useful for backups, application testing, and deploying VMs (Virtual Machines). The original state of the snapshot is kept as the block map.
Snapshots only use space for storing deltas:
- When the original logical volume changes, original data blocks are copied to the snapshot.
- If data is added to snapshot, it is stored only there.
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvcreate -l 128 -s -n mysnap /dev/myvgName/mylvmName
Logical volume "mysnap" created.
check snap
[s0x45ker--_(+_+)_--SysAdmin ~]$ df -Th | grep mysnap
/dev/mapper/myvgName-mysnap ext4 670M 2.5M 631M 1% /mnt
Delete Snapshot or Any LVM
[s0x45ker--_(+_+)_--SysAdmin ~]$ sudo lvremove /dev/myvgName/mysnap
Do you really want to remove active logical volume myvgName/mysnap? [y/n]: y
Logical volume "mysnap" successfully removed
comments powered by Disqus