- Introduction
- General information
- Physical volumes
- Volume groups
- Logical volumes
- Add space to a volume group
- Reduce space from an existing volume group
- Create a Snapshot of LVM
Introduction:
In this tutorial, I will show some LVM disk management commands in RHEL 6. LVM stands for logical volume manager. LVM allows you to create a logical storage volume using multiple physical disks. This has been tested in Red Hat Enterprise Linux 6.
General information
[asiface@linuxpathfinder ~]$ rpm -qa | grep -i lvm lvm2-libs-2.02.98-9.el6.i686 system-config-lvm-1.1.12-16.el6.noarch lvm2-2.02.98-9.el6.i686 [asiface@linuxpathfinder ~]$ sudo /sbin/fdisk -l | grep Disk [sudo] password: Disk /dev/sda: 16.1 GB, 16106127360 bytes Disk /dev/sdb: 10.7 GB, 10737418240 bytes Disk /dev/sdc: 5368 MB, 5368709120 bytes Display the local file system disk space usage. [asiface@linuxpathfinder ~]$ df -lh Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 11G 2.4G 83% / tmpfs 250M 228K 250M 1% /dev/shm /dev/sda1 291M 52M 224M 19% /boot /dev/sr1 3.0G 3.0G 0 100% /media/RHEL_6.4 i386 Disc 1
Physical volumes
/dev/sdb and /dev/sdc will make physical volumes.
[root@linuxpathfinder /]# fdisk /dev/sdb
WARNING: DOS-compatible mode is deprecated. It’s strongly recommended to
switch off the mode (command ‘c’) and change display units to
sectors (command ‘u’).
Command (m for help): p
Disk /dev/sdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xfd272a95
Device Boot Start End Blocks Id System
Command (m for help): m
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition’s system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-1305, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-1305, default 1305):
Using default value 1305
Command (m for help): p
Disk /dev/sdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xfd272a95
Device Boot Start End Blocks Id System
/dev/sdb1 1 1305 10482381 83 Linux
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): p
Disk /dev/sdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xfd272a95
Device Boot Start End Blocks Id System
/dev/sdb1 1 1305 10482381 8e Linux LVM
Command (m for help): w
The partition table has been altered!
Reboot needed after below mentioned command.
[root@linuxpathfinder /]# partprobe Warning: WARNING: the kernel failed to re-read the partition table on /dev/sda (Device or resource busy). As a result, it may not reflect all of your changes until after reboot. [root@linuxpathfinder /]# pvcreate /dev/sdb1 Physical volume “/dev/sdb1” successfully created [root@linuxpathfinder /]# pvs PV VG Fmt Attr PSize PFree /dev/sdb1 lvm2 a– 10.00g 10.00g [root@linuxpathfinder /]# pvdisplay “/dev/sdb1” is a new physical volume of “10.00 GiB” — NEW Physical volume — PV Name /dev/sdb1 VG Name PV Size 10.00 GiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID 1L2w2r-gIwi-QerY-8wo2-BLYp-pZPX-9qjs7H Another Physical Volume as shown below: [root@linuxpathfinder /]# pvs PV VG Fmt Attr PSize PFree /dev/sdb1 lvm2 a– 10.00g 10.00g /dev/sdc1 lvm2 a– 4.99g 4.99g [root@linuxpathfinder /]# pvdisplay “/dev/sdb1” is a new physical volume of “10.00 GiB” — NEW Physical volume — PV Name /dev/sdb1 VG Name PV Size 10.00 GiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID 1L2w2r-gIwi-QerY-8wo2-BLYp-pZPX-9qjs7H “/dev/sdc1” is a new physical volume of “4.99 GiB” — NEW Physical volume — PV Name /dev/sdc1 VG Name PV Size 4.99 GiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID dWQprr-Hagl-Vlf0-YLtL-paYn-Eeif-YmchY1
Volume groups
We have 2 physical volume which are sdb1 and sdc1. Now we will create Volume Group of both physical volumes.
[root@linuxpathfinder /]# vgcreate vg01 /dev/sdb1 /dev/sdc1 Volume group “vg01” successfully created
Attributes of volume group in which vg name is (VG01) as shown below.
[root@linuxpathfinder /]# vgs VG #PV #LV #SN Attr VSize VFree vg01 2 0 0 wz–n- 14.98g 14.98g [root@linuxpathfinder /]# vgdisplay — Volume group — VG Name vg01 System ID Format lvm2 Metadata Areas 2 Metadata Sequence No 1 VG Access read/write VG Status resizable MAX LV 0 Cur LV 0 Open LV 0 Max PV 0 Cur PV 2 Act PV 2 VG Size 14.98 GiB PE Size 4.00 MiB Total PE 3836 Alloc PE / Size 0 / 0 Free PE / Size 3836 / 14.98 GiB VG UUID larW0I-dris-BCNU-2Pb1-nNjv-wzEx-viGwry
Logical volumes
We will create 8 gigabyte logical volume in the following step.
[root@linuxpathfinder /]# lvcreate -L 8G -n lv01 vg01 Logical volume “lv01” created [root@linuxpathfinder /]# lvscan ACTIVE ‘/dev/vg01/lv01’ [8.00 GiB] inherit
Some commands to see logical volumes.
[root@linuxpathfinder /]# lvs LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert lv01 vg01 -wi-a—- 8.00g [root@localhost /]# [root@linuxpathfinder /]# lvdisplay — Logical volume — LV Path /dev/vg01/lv01 LV Name lv01 VG Name vg01 LV UUID Kz8Wxq-66hX-XUSC-t28z-Rkd7-f7yR-Y1h114 LV Write Access read/write LV Creation host, time localhost.localdomain, 2014-01-11 23:55:59 -0800 LV Status available # open 0 LV Size 8.00 GiB Current LE 2048 Segments 1 Allocation inherit Read ahead sectors auto – currently set to 256 Block device 253:0
Now we will create a file system on /dev/vg01/lv01 from the following steps.
[root@linuxpathfinder /]# mkfs.ext4 /dev/vg01/lv01 mke2fs 1.41.12 (17-May-2010) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 524288 inodes, 2097152 blocks 104857 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2147483648 64 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632 Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 30 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
Now create a folder which name let suppose (new_drive) and mount the logical volume on this folder.
[root@linuxpathfinder /]# mount -t ext4 /dev/vg01/lv01 /new_drive/
It will be successfully mounted.
[root@linuxpathfinder /]# df -ahl Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 11G 2.3G 83% / proc 0 0 0 – /proc sysfs 0 0 0 – /sys devpts 0 0 0 – /dev/pts tmpfs 250M 232K 250M 1% /dev/shm /dev/sda1 291M 52M 224M 19% /boot /dev/mapper/vg01-lv01 7.9G 146M 7.4G 2% /new_drive
After that we will add the following entry into /etc/fstab file.
[root@linuxpathfinder /]# vim /etc/fstab /dev/vg01/lv01 /new_drive ext4 defaults 0 0
Add space to a volume group
We will go through an example of adding more space to a volume group which name lv01. Steps are as follows:
[root@linuxpathfinder new_drive]# lvresize -L 11G /dev/vg01/lv01 Extending logical volume lv01 to 11.00 GiB Logical volume lv01 successfully resized [root@linuxpathfinder new_drive]#
But disk space will not extend or increase yet…. we will make with further more step.
[root@linuxpathfinder new_drive]# resize2fs /dev/vg01/lv01 resize2fs 1.41.12 (17-May-2010) Filesystem at /dev/vg01/lv01 is mounted on /new_drive; on-line resizing required old desc_blocks = 1, new_desc_blocks = 1 Performing an on-line resize of /dev/vg01/lv01 to 2883584 (4k) blocks. The filesystem on /dev/vg01/lv01 is now 2883584 blocks long.
Now see below the disk size is resized and increased space from 8G to 11G.
[root@linuxpathfinder new_drive]# df -ahl Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 11G 2.3G 83% / proc 0 0 0 – /proc sysfs 0 0 0 – /sys devpts 0 0 0 – /dev/pts /dev/sda1 291M 52M 224M 19% /boot /dev/mapper/vg01-lv01 11G 148M 11G 2% /new_drive
Reduce space From aN Existing Volume group
Now we will go through how to reduce the volume disk space. But before doing these steps please make sure you have taken backup of your data from your production server.
First we will unmount the file system and then run fsck command.
[root@linuxpathfinder /]# umount /new_drive/ [root@linuxpathfinder /]# fsck -f /dev/vg01/lv01 fsck from util-linux-ng 2.17.2 e2fsck 1.41.12 (17-May-2010) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/mapper/vg01-lv01: 12/720896 files (0.0% non-contiguous), 83136/2883584 blocks
After that we will go through vice versa. And we will reduce disk size from 11G to 6G.
Using resize2fs command:
[root@linuxpathfinder /]# resize2fs /dev/vg01/lv01 6G resize2fs 1.41.12 (17-May-2010) Resizing the filesystem on /dev/vg01/lv01 to 1572864 (4k) blocks. The filesystem on /dev/vg01/lv01 is now 1572864 blocks long.
Using lvresize command:
[root@linuxpathfinder /]# lvresize -L 6G /dev/vg01/lv01 WARNING: Reducing active logical volume to 6.00 GiB THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce lv01? [y/n]: y Reducing logical volume lv01 to 6.00 GiB Logical volume lv01 successfully resized
After successfully reduced the volume, we will again mount the lv file system.
[root@linuxpathfinder /]# mount -t ext4 /dev/vg01/lv01 /new_drive/
You can see the newly logical volume disk space from 11G to 6G.
[root@linuxpathfinder /]# df -lh Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 11G 2.3G 83% / /dev/sda1 291M 52M 224M 19% /boot /dev/mapper/vg01-lv01 6.0G 144M 5.5G 3% /new_drive
Note: We can also increase and decrease the disk space with lvextend and lvreduce command. But here I am using resize command. You can get more information from their (man) pages.
Create A Snapshot of LVM
The purpose of snapshot is to make backup of the lvm. If you lost some from existing lvm, don’t worry about it…. You can take data from a LVM snapshot.
How to create Snapshot of Logical Volume:
[root@linuxpathfinder /]# lvcreate -L 4G -s -n lvmsnapshot /dev/vg01/lv01 Logical volume “lvmsnapshot” created [root@linuxpathfinder /]# lvs LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert lv01 vg01 owi-aos– 6.00g lvmsnapshot vg01 swi-a-s– 4.00g lv01 0.00
To retrieve a data from lvmsnapshot, first we will mount lvmsnapshot as shown below.
[root@linuxpathfinder /]# mount -t ext4 /dev/vg01/lvmsnapshot /snapshot/ [root@linuxpathfinder /]# df -ah Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 11G 2.3G 83% / proc 0 0 0 – /proc /dev/sda1 291M 52M 224M 19% /boot /dev/mapper/vg01-lv01 6.0G 145M 5.5G 3% /new_drive /dev/mapper/vg01-lvmsnapshot 6.0G 145M 5.5G 3% /snapshot [root@linuxpathfinder /]# cd /snapshot/ [root@linuxpathfinder snapshot]# ls hosts lost+found services test1.txt [root@linuxpathfinder snapshot]# cp hosts /new_drive/ [root@linuxpathfinder snapshot]# cd /new_drive/ [root@linuxpathfinder new_drive]# ll total 648 -rw-r–r– 1 root root 158 Jan 12 02:26 hosts drwx—— 2 root root 16384 Jan 11 23:58 lost+found -rw-r–r– 1 root root 641020 Jan 12 01:55 services -rw-r–r– 1 root root 0 Jan 12 00:12 test1.txt
Using unmount and lvremove commands:
[root@linuxpathfinder new_drive]# umount /snapshot/ [root@linuxpathfinder new_drive]# lvremove /dev/vg01/lvmsnapshot Do you really want to remove active logical volume lvmsnapshot? [y/n]: y Logical volume “lvmsnapshot” successfully removed [root@linuxpathfinder new_drive]# lvs LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert lv01 vg01 -wi-ao— 6.00g
I hope you will be able to manage logical volume manager with above steps.
