LVM quickly explained:

In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes. In particular, a volume manager can concatenate, stripe together or otherwise combine partitions into larger virtual ones that administrators can re-size or move, potentially without interrupting system use.

As seen in the LVM design scheme, Physical Volumes (PV) are the bottom layer of LVM. The second layer are Volume Groups (VG) and the final, third layer are Logical Volumes (LV). In Part 1 (LVM – Physical Volume Management on CentOS 6) we learned how to manage PV’s and already prepared PV’s to be added to Volume Groups (VG’s). This example is continuation of Part 1 (LVM – Physical Volume Management on CentOS 6).

Here is the basic design scheme:

Volume Group Management is a part 2/3 of LVM Management on CentOS 6!

• Part 1 – LVM – Physical Volume Management on CentOS 6
• Part 2 – LVM – Volume Group Management on CentOS 6
• Part 3 – LVM – Logical Volume Management on CentOS 6

In this post we will learn how to create, delete, extend, reduce, rename, merge, split and change Volume Groups (VG). We will learn how to prepare Volume Groups for Logical Volumes.

Let’s start our Volume Group Management on CentOS 6 guide!

For this example we have 3 additional hard drives:/dev/sdb (1GB), /dev/sdc (2GB) and /dev/sdd (3GB). /dev/sda2 is a pre-existing PV on my system that holds the system root and swap partition.

1. Displaying Volume Groups

We can display all Volume Groups (VG’s) on the system with the “vgdisplay” command:

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

We can also display Volume Groups with “vgscan” or “vgs” commands, but as we see the output is a bit different – in following example i will be using “vgdisplay“, because it gives me the most info:

[root@foo ~]# vgscan
 Reading all physical volumes. This may take a while...
 Found volume group "vg_foo" using metadata type lvm2

[root@foo ~]# vgs
 VG #PV #LV #SN Attr VSize VFree
 vg_foo 1 2 0 wz--n- 14.51g 0

We see there is currently only one existing Volume Group present. This VG is called vg_foo and is the VG, that holds the system root and swap partition. With the “vgdisplay” command we se additional info – VG size, PE size, Total PE,… This is the Physical Extent. A number of Physical Extents builds the Physical Volume.

2. Adding a Physical Volume to Volume Groups

We add PV’s to Volume Groups (VG’s) using “vgcreate name /dev/harddisk” command. It is very simple, no additional parameters are needed. Let’s see an example of creating a new VG called “geekpeek” and add /dev/sdb and /dev/sdc PV’s to it:

[root@foo ~]# vgcreate geekpeek /dev/sdb /dev/sdc
 Volume group "geekpeek" successfully created

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name geekpeek
 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 2.99 GiB
 PE Size 4.00 MiB
 Total PE 766
 Alloc PE / Size 0 / 0
 Free PE / Size 766 / 2.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

We can see that VG was successfully created. We can also see the full state of the “geekpeek” VG – VG size, Total PE, PE size, …

3. Extending Volume Groups

We can extend a Volume Group with “vgextend” command. The simple syntax is “vgextend name /dev/harddisk“. By extending VG you add PV’s to it and extend VG’s size. In our example we will extend VG called “geekpeek” from 2.99GB to 5.99GB by adding /dev/sdd PV:

[root@foo ~]# vgextend geekpeek /dev/sdd
 Volume group "geekpeek" successfully extended

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name geekpeek
 System ID
 Format lvm2
 Metadata Areas 3
 Metadata Sequence No 2
 VG Access read/write
 VG Status resizable
 MAX LV 0
 Cur LV 0
 Open LV 0
 Max PV 0
 Cur PV 3
 Act PV 3
 VG Size 5.99 GiB
 PE Size 4.00 MiB
 Total PE 1533
 Alloc PE / Size 0 / 0
 Free PE / Size 1533 / 5.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

4. Reducing Volume Groups

We can reduce a Volume Group with “vgreduce” command. The simple syntax is “vgreduce name /dev/harddisk“. By reducing VG you remove PV’s from it and reduce VG’s size. In our example we will reduce VG called “geekpeek” from 5.99GB to 2.99GB by removing /dev/sdd PV:

[root@foo ~]# vgreduce geekpeek /dev/sdd
 Removed "/dev/sdd" from volume group "geekpeek"

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name geekpeek
 System ID
 Format lvm2
 Metadata Areas 2
 Metadata Sequence No 5
 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 2.99 GiB
 PE Size 4.00 MiB
 Total PE 766
 Alloc PE / Size 0 / 0
 Free PE / Size 766 / 2.99 GiB
 VG UUID i339tr-lqNb-OKra-1FE2-UZ82-A1TI-t8w7BT

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

5. Splitting Volume Groups

We can split Volume Group with “vgsplit” command. The simple syntax is “vgsplit name newname /dev/harddisk“. By splitting VG you remove PV’s from it and reduce VG’s size. In our example we will split VG called “geekpeek” and create a new VG called “splitgeek“:

[root@foo ~]# vgsplit geekpeek splitgeek /dev/sdd
 New volume group "splitgeek" successfully split from "geekpeek"

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name splitgeek
 System ID
 Format lvm2
 Metadata Areas 1
 Metadata Sequence No 2
 VG Access read/write
 VG Status resizable
 MAX LV 0
 Cur LV 0
 Open LV 0
 Max PV 0
 Cur PV 1
 Act PV 1
 VG Size 3.00 GiB
 PE Size 4.00 MiB
 Total PE 767
 Alloc PE / Size 0 / 0
 Free PE / Size 767 / 3.00 GiB
 VG UUID 1ZvPM3-3jgO-0t1e-r4I1-Sxw2-vhUM-clGQLg

--- Volume group ---
 VG Name geekpeek
 System ID
 Format lvm2
 Metadata Areas 2
 Metadata Sequence No 3
 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 2.99 GiB
 PE Size 4.00 MiB
 Total PE 766
 Alloc PE / Size 0 / 0
 Free PE / Size 766 / 2.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

6. Merging Volume Groups

In the next step we will merge the split Volume Groups (VG’s) back together. We can merge VG’s with “vgmerge” command. The simple syntax is “vgmerge name1 name2“:

[root@foo ~]# vgmerge geekpeek splitgeek
 Volume group "splitgeek" successfully merged into "geekpeek"

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name geekpeek
 System ID
 Format lvm2
 Metadata Areas 3
 Metadata Sequence No 4
 VG Access read/write
 VG Status resizable
 MAX LV 0
 Cur LV 0
 Open LV 0
 Max PV 0
 Cur PV 3
 Act PV 3
 VG Size 5.99 GiB
 PE Size 4.00 MiB
 Total PE 1533
 Alloc PE / Size 0 / 0
 Free PE / Size 1533 / 5.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

7. Changing Volume Groups

We can change Volume Group parameters with “vgchange” command. The simple syntax is “vgchange name -parameter value“. By changing VG’s you can change VG’s parameters – check “vgchange –help” for more info. In our example we will change PE size of our VG called “geekpeek“:

[root@foo ~]# vgchange geekpeek -s 2048KB
 Volume group "geekpeek" successfully changed

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name geekpeek
 System ID
 Format lvm2
 Metadata Areas 3
 Metadata Sequence No 8
 VG Access read/write
 VG Status resizable
 MAX LV 0
 Cur LV 0
 Open LV 0
 Max PV 0
 Cur PV 3
 Act PV 3
 VG Size 5.99 GiB
 PE Size 2.00 MiB
 Total PE 3066
 Alloc PE / Size 0 / 0
 Free PE / Size 3066 / 5.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

We can see that we have successfully changed Total PE size of VG from 4.00MBiB to 2.00MiB.

8. Remaning Volume Groups

We can rename Volume Group with “vgrename” command. The simple syntax is “vgrename name1 name2“. In our example we will rename our VG called “geekpeek” to “renamegeek“:

[root@foo ~]# vgrename geekpeek renamegeek
 Volume group "geekpeek" successfully renamed to "renamegeek"

[root@foo ~]# vgdisplay
 --- Volume group ---
 VG Name renamegeek
 System ID
 Format lvm2
 Metadata Areas 3
 Metadata Sequence No 9
 VG Access read/write
 VG Status resizable
 MAX LV 0
 Cur LV 0
 Open LV 0
 Max PV 0
 Cur PV 3
 Act PV 3
 VG Size 5.99 GiB
 PE Size 2.00 MiB
 Total PE 3066
 Alloc PE / Size 0 / 0
 Free PE / Size 3066 / 5.99 GiB
 VG UUID oj2GS6-l5aE-6WNv-QPJy-r1pC-ahSQ-EzFiKc

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

We can see that we have successfully renamed VG “geekpeek” to “renamegeek“.

9. Removing Volume Groups

We can remove Volume Groups (VG’s) with “vgremove” command. The simple syntax is “vgremove name“. In our example we will remove VG called “geekpeek“:

[root@foo ~]# vgremove geekpeek
 Volume group "geekpeek" successfully removed.

[root@foo ~]# vgdisplay

--- Volume group ---
 VG Name vg_foo
 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 14.51 GiB
 PE Size 4.00 MiB
 Total PE 3714
 Alloc PE / Size 3714 / 14.51 GiB
 Free PE / Size 0 / 0
 VG UUID 3n3nzs-dzHK-rApY-EApz-Zz2H-JQVP-TlcYfF

Before you manage your Volume Groups make appropriate reconfiguration of the Logical Volumes! If not, you can loose or corrput your data!