LVM
is a tool for logical volume management which is used to allocating
disks, striping, mirroring and resizing logical volumes. With LVM, a
hard drive or set of hard drives is allocated to one or more physical
volumes. LVM physical volumes can be placed on other block devices
which might span two or more disks. Since a physical volume cannot
span over multiple drives, to span over more than one drive, create
one or more physical volumes per drive. The volume groups can be
divided into logical volumes, which are assigned mount points, such
as
/home
and /
and file system types, such as ext2 or ext3 or ext4. When
“partitions” reach their full capacity, free space from the
volume group can be added to the logical volume to increase the size
of the partition. When a new hard drive is added to the system, it
can be added to the volume group, and partitions that are logical
volumes can be increased in size.
On
the other hand, if a system is partitioned with the ext4 file system,
the hard drive is divided into partitions of defined sizes. If a
partition becomes full, it is not easy to expand the size of the
partition. Even if the partition is moved to another hard drive, the
original hard drive space has to be reallocated as a different
partition or not used.
In
this how-to tutorial let us learn some basics of LVM commands.
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): +100MTo 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 LinuxSave 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
Note:
If you had installed the server in the minimal mode, the commands
pvcreate, lvcreate, vgcreate etc., couldn’t be found. To use that
commands install the lvm2 package first.
[root@server ~]# yum install lvm2 Loaded plugins: rhnplugin This system is not registered with RHN. RHN support will be disabled. Setting up Install ProcessThe Resolving Dependencies --> Running transaction check ---> Package lvm2.i686 0:2.02.72-8.el6 set to be updated --> Processing Dependency: lvm2-libs = 2.02.72-8.el6 for package: lvm2-2.02.72-8.el6.i686 --> Processing Dependency: libdevmapper-event.so.1.02(Base) for package: lvm2-2.02.72-8.el6.i686 --> Processing Dependency: libdevmapper-event.so.1.02 for package: lvm2-2.02.72-8.el6.i686 --> Running transaction check ---> Package device-mapper-event-libs.i686 0:1.02.53-8.el6 set to be updated ---> Package lvm2-libs.i686 0:2.02.72-8.el6 set to be updated --> Processing Dependency: device-mapper-event >= 1.02.53-8.el6 for package: lvm2-libs-2.02.72-8.el6.i686 --> Running transaction check ---> Package device-mapper-event.i686 0:1.02.53-8.el6 set to be updated --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: lvm2 i686 2.02.72-8.el6 localrepo 514 k Installing for dependencies: device-mapper-event i686 1.02.53-8.el6 localrepo 79 k device-mapper-event-libs i686 1.02.53-8.el6 localrepo 74 k lvm2-libs i686 2.02.72-8.el6 localrepo 565 k Transaction Summary ================================================================================ Install 4 Package(s) Upgrade 0 Package(s) Total download size: 1.2 M Installed size: 2.5 M Is this ok [y/N]: y Downloading Packages: -------------------------------------------------------------------------------- Total 11 MB/s | 1.2 MB 00:00 Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction Installing : device-mapper-event-libs-1.02.53-8.el6.i686 1/4 Installing : device-mapper-event-1.02.53-8.el6.i686 2/4 Installing : lvm2-libs-2.02.72-8.el6.i686 3/4 Installing : lvm2-2.02.72-8.el6.i686 4/4 Installed: lvm2.i686 0:2.02.72-8.el6 Dependency Installed: device-mapper-event.i686 0:1.02.53-8.el6 device-mapper-event-libs.i686 0:1.02.53-8.el6 lvm2-libs.i686 0:2.02.72-8.el6 Complete!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 createdTo 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 createdTo 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" createdVerify 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
Extend Volume Group Size
If
you’re running out of the space in the logical volume, you can
extend the size of it easily if your physical disk contains free
space or with additional physical disk(Hard disk).
Say
for example let us extend the volume group vg1 using
the physical volume /dev/sdb3. And let us add additonal
100MB to logical volume lv1.
[root@server mnt]# vgextend vg1 /dev/sdb3 Volume group "vg1" successfully extendedThen resize the logical vloume lv1.
[root@server mnt]# lvresize -L +100M /dev/vg1/lv1 Extending logical volume lv1 to 300.00 MiB Logical volume lv1 successfully resizedResize the filesystem of logical volume lv1.
[root@server mnt]# resize2fs /dev/vg1/lv1 resize2fs 1.41.12 (17-May-2010) Filesystem at /dev/vg1/lv1 is mounted on /mnt; on-line resizing required old desc_blocks = 1, new_desc_blocks = 2 Performing an on-line resize of /dev/vg1/lv1 to 307200 (1k) blocks. The filesystem on /dev/vg1/lv1 is now 307200 blocks long.Now verify the new size of the logical volume lv1.
[root@server mnt]# lvdisplay /dev/vg1/lv1 --- 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 1 LV Size 300.00 MiB Current LE 75 Segments 3 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 253:0It’s done. Now the size of the logical volume lv1 is extended by 100MB.
Remove Logical Volume
Come
out of the /mnt mount point, unmount the logical volume
lv1 and remove it using command lvremove.
[root@server mnt]# cd .. [root@server /]# umount /mnt/ [root@server /]# lvremove /dev/vg1/lv1 Do you really want to remove active logical volume lv1? [y/n]: y Logical volume "lv1" successfully removed
Remove Volume Group
[root@server /]# vgremove /dev/vg1 Volume group "vg1" successfully removed
Remove Physical Volume
[root@server /]# pvremove /dev/sdb1 /dev/sdb2 /dev/sdb3 Labels on physical volume "/dev/sdb1" successfully wiped Labels on physical volume "/dev/sdb2" successfully wiped Labels on physical volume "/dev/sdb3" successfully wiped
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