Over the last two days I've had the interesting task of online some VMs from clones and increasing their disk space to accommodate a mass of user uploaded content. I've done this before but never actually with an Logical Volume Management (LVM) disk.

My first approach, like a fool, was to clone the VM from source and boot it from a remotely mounted GParted ISO, this didn't actually go as expected and I was unable to add it to the LVM, I found a nice guide online and consulted a colleague because I knew he'd done something similar recently. After the first successful size increase I realised I was able to do it without ever rebooting the machine itself, this is accomplished by actually adding an extra disk to the VM, this disk can then be partition with cfdisk and then added to the LVM, thus increasing disk space without the need to resize the actual main disk. The LVM doesn't care if the disks are physically separate (in this case they aren't, they're on the same SAN but are still seen by the OS as being different devices), as far as the LVM is concerned it will actually just make them appear to the OS as one disk, even though made up from different parts.

So, onwards.

Assigning the additional space to the VM

This is rather easy, I'm going to assume anyone that is reading this guide has VMWare installed, their host and guests configured properly. etc. This guide is also aimed at ESX but is still easily applicable to ESXi, VMWare player, etc.

Within ESX, modify your VMs settings, adding an additional SCSI hard disk, I'm going to give mine an additional drive with 210GB of space.

Partitioning the newly added space

Once done, go to your VM, and as root run the following command:

echo "- - -" > /sys/class/scsi_host/host0/scan && fdisk -l

If the newly added unpartitioned drive isn't displayed, try again with a different host# - host1, host2 etc.

cfdisk /dev/sda

If you don't have cfdisk installed, you should be able to install it with the following command on Debian-based systems:

apt-get install cfdisk

Once you have it running the ASCII interface should be simple to follow, select your unallocated space and partition it, making sure you select it's type as Logical Volume (8E) and not set it as bootable. Write these changes and close cfdisk.

Name Flags Part Type FS Type [Label] Size (MB)
------------------------------------------------------------------------------
sda1 Boot Primary Linux ext3 254.99
sda5 Logical Linux LVM 10479.01
sda6 Logical Linux LVM 225487.83

Adding to an existing LVM

Lets take a look at our current list of physical volumes

pvs

PV VG Fmt Attr PSize PFree
/dev/sda5 jeos-base lvm2 a- 9.76G 0

As you can see we have our existing list of volumes, in my case one.

So now all we need to do is create another physical volume, my partition is labelled sda6 so that's what I will be using.

pvcreate /dev/sda6

Now that we've added the volume it's time to add it to the volume group, this is really simple and again I'll be using sda6.

vgextend jeos-base /dev/sda6

jeos-root is the name of my volume group, you'd obviously replace this with your own groups name.

Now if we actually take a look at pvs again you will see that your physical volume has been created and added to your volume group.

pvs && lvdisplay

PV VG Fmt Attr PSize PFree
/dev/sda5 jeos-base lvm2 a- 9.76G 0
/dev/sda6 lvm2 -- 210.00G 0

--- Logical volume ---
LV Name /dev/jeos-base/root
VG Name jeos-base
LV UUID 1234
LV Write Access read/write
LV Status available
# open 1
LV Size 9.76 GB
Current LE 12620
Segments 2
Allocation inherit
Read ahead sectors 0
Block device 254:0

The first output shows that your device has been added to the volume group, the second output will show you that it isn't actually added to the LVM, so the next step is to actually extend the LVM

Thanks to Ivan Marinkovic from the comments for this improved command:

lvextend -l+100%FREE /dev/jeos-base/root && lvdisplay

--- Logical volume ---
LV Name /dev/jeos-base/root
VG Name jeos-base
LV UUID 1234
LV Write Access read/write
LV Status available
# open 1
LV Size 219.30 GB
Current LE 56140
Segments 2
Allocation inherit
Read ahead sectors 0
Block device 254:0

With the output of lvextend you will see that it successfully extending the logical volume and lvdisplay should confirm that.

Resizing the file system

Now that we have the LVM extended we will actually want to extend the file system too, so that it can use the full extra space freely, this can be done online, I'd recommend doing a snapshot or backup of your VM before doing this though.

resize2fs /dev/mapper/jeos--base-root && df -h

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/jeos--base-root
218G 1.7G 205G 1% /

And that's it, all done. The output of df should confirm that your free space has now increased in size.

Credits

  1. Original guide that I partially followed with a colleague -- http://www.randombugs.com/linux/howto-extend-lvm-partition-online.html
  2. Federico Marani, the colleague that helped - http://marro.wordpress.com/ (Italian)
  3. Thanks to Mike Heald for linking me to reloading SCSI list