Logical Volume Manager (LVM)
This article describes a basic logic behind a Linux logical volume manager by showing real examples of configuration and usage. Although Debian Linux will be used for this tutorial, you can also apply the same command line syntax with other Linux distributions such as Red Hat, Mandriva, SuSe Linux and others.
1. This is what we are going to do
Scenario:
In this example let us
- Create 3 partitions of size each 100MB.
- Convert them into physical volumes.
- Combine physical volumes into volume group.
- Finally create a logical volume from the volume group.
Create Partitions
Use fdisk command to create and manage partions.
To view the existing partitions use following command
[root@server ~]# fdisk -l Disk /dev/sdb: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 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: 0x0007b12c Device Boot Start End Blocks Id System Disk /dev/sda: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 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: 0x000ac451 Device Boot Start End Blocks Id System /dev/sda1 * 1 128 1024000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 128 291 1310720 82 Linux swap / Solaris Partition 2 does not end on cylinder boundary. /dev/sda3 291 1045 6052864 83 Linux
The above output shows us two physical hard disks. The /dev/sda contains three partitions and no space to create additional partions. And the second drive /dev/sdb contains no partions yet. So let us use the second one in this tutorial.
Now let us create three partions of each size 100MB using fdisk command.
[root@server ~]# 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): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-1044, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-1044, default 1044): +100M
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (15-1044, default 15):
Using default value 15
Last cylinder, +cylinders or +size{K,M,G} (15-1044, default 1044): +100M
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 3
First cylinder (29-1044, default 29):
Using default value 29
Last cylinder, +cylinders or +size{K,M,G} (29-1044, default 1044): +100M
To check whether the partions have been created use the parameter “p”.
Command (m for help): p Disk /dev/sdb: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 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: 0x0007b12c Device Boot Start End Blocks Id System /dev/sdb1 1 14 112423+ 83 Linux /dev/sdb2 15 28 112455 83 Linux /dev/sdb3 29 42 112455 83 Linux
Save the newly created partions.
Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
Update the kernel to save the changes without restarting the system.
[root@server ~]# 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.
Again we will check the existing partitions using fdisk command.
[root@server ~]# fdisk -l Disk /dev/sdb: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 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: 0x0007b12c Device Boot Start End Blocks Id System /dev/sdb1 1 14 112423+ 83 Linux /dev/sdb2 15 28 112455 83 Linux /dev/sdb3 29 42 112455 83 Linux Disk /dev/sda: 8589 MB, 8589934592 bytes 255 heads, 63 sectors/track, 1044 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: 0x000ac451 Device Boot Start End Blocks Id System /dev/sda1 * 1 128 1024000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 128 291 1310720 82 Linux swap / Solaris Partition 2 does not end on cylinder boundary. /dev/sda3 291 1045 6052864 83 Linux
The above output shows three partions has been created in the /dev/sdb disk. If fdisk -l doesn’t show the output reboot to take effect.
Create Physical Volumes
Now create physical volumes using the command pvcreate.
[root@server ~]# pvcreate /dev/sdb1 /dev/sdb2 /dev/sdb3 Physical volume "/dev/sdb1" successfully created Physical volume "/dev/sdb2" successfully created Physical volume "/dev/sdb3" successfully created
We can use like this also
[root@server ~]# pvcreate /dev/sdb{1,2,3}
To verify the newly created physical volumes use the command pvdisplay.
[root@server ~]# pvcreate /dev/sdb{1,2,3}
To verify the newly created physical volumes use the command pvdisplay.
[root@server ~]# pvdisplay "/dev/sdb1" is a new physical volume of "109.79 MiB" --- NEW Physical volume --- PV Name /dev/sdb1 VG Name PV Size 109.79 MiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID jQl5F4-DyLj-SkHu-4lhZ-J3nQ-zax9-aT8sc4 "/dev/sdb2" is a new physical volume of "109.82 MiB" --- NEW Physical volume --- PV Name /dev/sdb2 VG Name PV Size 109.82 MiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID i4MHvw-8hYB-Fwz8-fxTL-G3mu-fl5E-zGYhDO "/dev/sdb3" is a new physical volume of "109.82 MiB" --- NEW Physical volume --- PV Name /dev/sdb3 VG Name PV Size 109.82 MiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID 99qkNw-3oAw-vXwg-WE6U-zyKO-Ffs3-rDSqUY
Create Volume Groups
Create a new volume group called vg1 using two physical volumes /dev/sdb1 and /dev/sdb2 using the command vgcreate.
[root@server ~]# vgcreate vg1 /dev/sdb1 /dev/sdb2 Volume group "vg1" successfully created
We can use like this also
[root@server ~]# vgcreate vg1 /dev/sdb{1,2}
To verify the volume group has been created or not use the command vgdisplay.
[root@server ~]# vgcreate vg1 /dev/sdb{1,2}
To verify the volume group has been created or not use the command vgdisplay.
[root@server ~]# vgdisplay --- Volume group --- VG Name vg1 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 216.00 MiB PE Size 4.00 MiB Total PE 54 Alloc PE / Size 0 / 0 Free PE / Size 54 / 216.00 MiB VG UUID ds3OtP-DMUx-33nN-HDar-eqNj-uIED-41gjqI
Create Logical Volume
To create logical volume use the command lvcreate. Let us create a logical volume called lv1 with size 200MB.
[root@server ~]# lvcreate -L 200M vg1 -n lv1 Logical volume "lv1" created
Verify the logical volume is created or not using command lvdisplay.
[root@server ~]# lvdisplay --- Logical volume --- LV Name /dev/vg1/lv1 VG Name vg1 LV UUID dgLZ79-JZdn-NUSF-fUS1-YVFk-36qs-iuafhE LV Write Access read/write LV Status available # open 0 LV Size 200.00 MiB Current LE 50 Segments 2 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 253:0
Format and Mount the logical volume
Now format the newly created logical volume and mount it in the /mnt directory or wherever you want.
[root@server ~]# mkfs.ext4 /dev/vg1/lv1
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
51200 inodes, 204800 blocks
10240 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
25 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
And mount the logical volume in the /mnt mount point.
[root@server ~]# mount /dev/vg1/lv1 /mnt/
Now the logical volume is successfully mounted in /mnt. You can use the new logical volume to store your datas.
[root@server ~]# cd /mnt/ [root@server mnt]# touch file1 file2 file3 [root@server mnt]# mkdir dir1 dir2 dir3 [root@server mnt]# ls dir1 dir2 dir3 file1 file2 file3 lost+found
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