An example LVM diagram:
The idea of LVM is it abstracts the logical volume away from the physical volume, such that multiple physical volumes will appear to the user a single continuous logical volume.
The root file system is in /dev/file-server-vg/root and the swap is in /dev/file-server-vg/swap. The idea is we can actually have multiple real hard disks in the PV layer, and they can be all added into a Volume Group, which will allow them to all appear as a single continuous file system to the system at /dev/file-server-vg/root.
In this problem I have been using /dev/file-server-vg/root as a file server and it is running out of space. Luckily this system is on a virtual machine, and I was able to expand the physical volume /dev/sda using the virtual machine manager. However, the increase in size doesn’t get automatically passed to the /dev/file-server-vg/root file system. We need to do a few simple command to get this to work.
Before we start, use pvdisplay to see which physical volumes are present. This will list all the physical volumes and the volume group that it belongs to. In this case we only have one physical volume that is /dev/sda3.
--- Physical volume ---
PV Name /dev/sda3
VG Name file-server-vg
PV Size 155.26 GiB / not usable 0
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 65346
Free PE 0
Allocated PE 65346
PV UUID 0EXhc4-EoHZ-b79R-ncSe-SWXI-ztPe-Fsc7zk
The current partition table can be listed by using sudo parted and then print.
Number Start End Size File system Name Flags
1 1049kB 538MB 537MB fat32 boot
2 538MB 794MB 256MB ext2
3 794MB 167GB 166GB lvm
In this example we want to expand the capacity from 155.56GiB to 255.56GiB. Using the virtual machine manager we can usually extend the disk space, and in this case we will expand it by 100GiB.
After expansion is successful, the resulting partition table (use print free) will look like the following. Please note the “Free space” shows 108GB (~100GiB).
Number Start End Size File system Name Flags
1 1049kB 538MB 537MB fat32 boot
2 538MB 794MB 256MB ext2
3 794MB 275GB 166GB lvm
167GB 275GB 108GB Free Space
There are two way to expand the logical volume:
Create a new partition and add this to the Volume Group, or
Increase the same partition.
In my opinion, where possible, the second method is neater. Of course if /dev/sda3 is a physical hard disk, and you bought another hard disk to expand the space, then it will be logical to use the first method.
In parted type resize 3 794MB 275GB will resize partition 3 to take up all the free space, well almost:
Number Start End Size File system Name Flags
17.4kB 1049kB 1031kB Free Space
1 1049kB 538MB 537MB fat32 boot
2 538MB 794MB 256MB ext2
3 794MB 275GB 274GB lvm
275GB 275GB 1032kB Free Space
This is good enough, just 1MB not being used.
Next we will reboot the machine. This is needed to refresh the partition table.
What you will see now is that the physical volume has increased in size with pvdisplay
--- Physical volume ---
PV Name /dev/sda3
VG Name file-server-vg
PV Size 255.26 GiB / not usable 0
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 65346
Free PE 0
Allocated PE 65346
PV UUID 0EXhc4-EoHZ-b79R-ncSe-SWXI-ztPe-Fsc7zk
This increase in size will be automatically passed to the volume group, using vgdisplay you get the following. Please note vgextend doesn’t actually do what you might think it does. It doesn’t take up the free space, instead it is used for adding new physical volumes to a particular volume group.
--- Volume group ---
VG Name file-server-vg
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 5
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 255.26 GiB
PE Size 4.00 MiB
Total PE 65346
Alloc PE / Size 65346 / 255.26 GiB
Free PE / Size 0 / 0
VG UUID NwwIgT-W0SH-aeTe-d078-hcxx-XZ6W-QfnSA0
The logical volume doesn’t increase in size automatically. This is actually makes sense because the computer has no idea which logical volume you want to increase in size, or perhaps you want to create a new logical volume with the extra space in the volume group. So with lvdisplay you will see the following table, showing the /dev/file-server-vg/root only has 153.26GiB, but don’t worry we are very close.
--- Logical volume ---
LV Path /dev/file-server-vg/root
LV Name root
VG Name file-server-vg
LV UUID l6qvYZ-AmYw-tdgi-2jUu-XNB2-gecQ-6fDPt8
LV Write Access read/write
LV Creation host, time file-server, 2014-07-10 14:54:58 +1000
LV Status available
# open 1
LV Size 153.26 GiB
Current LE 64834
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:0
--- Logical volume ---
LV Path /dev/file-server-vg/swap_1
LV Name swap_1
VG Name file-server-vg
LV UUID OohMkN-rGLa-fM4M-6he2-MbM9-BBc3-Ck2Hs5
LV Write Access read/write
LV Creation host, time file-server, 2014-07-10 14:54:58 +1000
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:1
The way to increase the logical volume is to use lvextend -L +100GB /dev/file-server-vg/root
After that expand the file system with resize2fs /dev/file-server-vg/root
And you are done. You can do lvdisplay to check that the /dev/file-server-vg/root volume has extended to 253.26GiB
--- Logical volume ---
LV Path /dev/file-server-vg/root
LV Name root
VG Name file-server-vg
LV UUID l6qvYZ-AmYw-tdgi-2jUu-XNB2-gecQ-6fDPt8
LV Write Access read/write
LV Creation host, time file-server, 2014-07-10 14:54:58 +1000
LV Status available
# open 1
LV Size 253.26 GiB
Current LE 64834
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:0
--- Logical volume ---
LV Path /dev/file-server-vg/swap_1
LV Name swap_1
VG Name file-server-vg
LV UUID OohMkN-rGLa-fM4M-6he2-MbM9-BBc3-Ck2Hs5
LV Write Access read/write
LV Creation host, time file-server, 2014-07-10 14:54:58 +1000
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:1
Best Answer
The whole point of volume groups is to contain several logical volumes. The only reason I can think of to use separate volume groups is if they must be kept on different (sets of) physical volumes (for example, I have a desktop machine with two hard drives and three volume groups: one RAID1-ed between the two drives, and one on each drive).
If you only intend to run Linux on that machine, make a single partition on the hard disk, use that partition as a PV, make a VG containing just that PV, and create one LV per filesystem (root, home, swap).