Hello there.
Today I want to take a look at how to resize a virtual machine that uses LVM for its vdisks. As I mentioned in a post before, I am using primarily LVM for VMs on my servers. This makes resizing the disks a bit more of a process though.
The server I am using as an example is running CentOS 7, but this should not really matter. The steps should be identical to other distributions.
Let’s take a look.
List VMs and LVs
First, let’s take a look at what we are working with. As an example, I will be using my router/server which is running nextcloud as a VM. The important parts are highlighted in red.
List KVM pools and volumes
The first command shows the pools.
kvm-router :: ~ » sudo virsh pool-list Name State Autostart ------------------------------------------- default active yes ISO active yes Virtual_Machines active yes
We have the pool names, now we can list the volumes that are attached to the VMs. All of my VMs are in the “Virtual_Machines” pool.
kvm-router :: ~ » sudo virsh vol-list Virtual_Machines Name Path ------------------------------------------------------------------------------ nextcloud /dev/VM/nextcloud opnsense /dev/VM/opnsense paperless /dev/VM/paperless pihole /dev/VM/pihole
Good. We now know which disk we need to extend. /dev/VM/nextcloud in my case.
List LVM VGs and LVs
I also want to know if I have enough space left on my disk, to actually resize the VM.
kvm-router :: ~ » sudo vgs VG #PV #LV #SN Attr VSize VFree EXTERNAL-BACKUP 1 1 0 wz--n- <465.76g 0 VM 1 4 0 wz--n- <180.00g <94.00g centos 1 2 0 wz--n- <33.88g 4.00m
As we can see, the volume group has 94GB of free space left. I only need 3GB for the VM right now, so it’s more than enough.
We don’t really need this information, but still. Let’s take a look at the logical volumes.
kvm-router :: ~ » sudo lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert EXT-BACKUP EXTERNAL-BACKUP -wi-a----- <465.76g nextcloud VM -wi-ao---- 40.00g opnsense VM -wi-ao---- 9.00g paperless VM -wi-ao---- 20.00g pihole VM -wi-ao---- 17.00g root centos -wi-ao---- 30.00g swap centos -wi-a----- <3.88g
Nextcloud currently uses 40GB. We will extend it to 43GB.
Resizing the LV on the Host
Now we can begin the resizing process. First, we will grow the LV, after this, we need to inform the VM that the disk size actually changed. Once that’s done, we can SSH into the VM and resize the filesystem.
Growing the LV
I will only give 3 additional GB to the VM. I tend to keep the steps really small since it’s quite simple to grow the filesystem. Shrinking it is a bit of a hassle, if even at all possible.
Beginning with the logical volume. For the path, we use the information we gather from the “virsh vol-list” command.
kvm-router :: ~ » sudo lvextend -L +3G /dev/VM/nextcloud Size of logical volume VM/nextcloud changed from 40.00 GiB (10240 extents) to 43.00 GiB (11008 extents). Logical volume VM/nextcloud successfully resized.
Inform the VM
Now we need to inform the VM, otherwise, it won’t know about the new disk size. A reboot should also do, though I never tried it.
The “domain” is the name of the VM. We could also use the ID that we get with the “sudo virsh list” command.
kvm-router :: ~ » sudo blockresize --domain nextcloud --path /dev/VM/nextcloud --size +3G Block device '/dev/VM/nextcloud' is resized
Let us take another look at the logical volume size.
kvm-router :: ~ » sudo lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert EXT-BACKUP EXTERNAL-BACKUP -wi-a----- <465.76g nextcloud VM -wi-ao---- 43.00g opnsense VM -wi-ao---- 9.00g ....
43GB. Great. Now we can log in to the VM and resize the filesystem.
Resizing the LV and filesystem within the VM
SSH into the VM and take a look at the disk size.
fedora-kde :: ~ » ssh nextcloud
nextcloud :: ~ » lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sr0 11:0 1 1024M 0 rom vda 252:0 0 43G 0 disk ├─vda1 252:1 0 1G 0 part /boot └─vda2 252:2 0 39G 0 part ├─cl_nextcloud-root 253:0 0 37G 0 lvm / └─cl_nextcloud-swap 253:1 0 2G 0 lvm
We can see that the disk has 43GB. Since I am using LVM almost everywhere, I have to resize the second partition first (vda2) and then resize the logical volume.
Let’s start with that.
Recreating the partition and informing LVM
The next few steps will “delete” and recreate the partition. It’s more the information of the partition, than the actual partition itself. This sounds way more dangerous than it actually is. But still, you should always have backups.
This will be a bit hard to read, so every input will be marked purple.
nextcloud :: ~ » sudo fdisk /dev/vda Welcome to fdisk (util-linux 2.32.1). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): p Disk /dev/vda: 43 GiB, 46170898432 bytes, 90177536 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x33f2a5cd Device Boot Start End Sectors Size Id Type /dev/vda1 * 2048 2099199 2097152 1G 83 Linux /dev/vda2 2099200 83886079 81786880 39G 83 Linux
Delete the “root” partition. This is “vda2” in my case. Make a note of the “Start” sector marked red. We will need this for the recreation. Normally this will be set correctly automatically.
Command (m for help): d Partition number (1,2, default 2): 2 Partition 2 has been deleted.
Next, recreate the partition.
As we can see, the “first sector” is set correctly to 2099200. The “last sector” should be larger than before, which is also correct.
Do not remove the LVM2 signature.
Command (m for help): n Partition type p primary (1 primary, 0 extended, 3 free) e extended (container for logical partitions) Select (default p): p Partition number (2-4, default 2): 2 First sector (2099200-90177535, default 2099200): Last sector, +sectors or +size{K,M,G,T,P} (2099200-90177535, default 90177535): Created a new partition 2 of type 'Linux' and of size 42 GiB. Partition #2 contains a LVM2_member signature. Do you want to remove the signature? [Y]es/[N]o: N
Ok. Let’s take another look at the partitions. If it looks good (which it does in this case), we can write the configuration to disk with “w”.
Keep in mind that until you write the changes to the disk, nothing actually happened. So you can still back out, by typing “q” to quit “fdisk”.
Command (m for help): p Disk /dev/vda: 43 GiB, 46170898432 bytes, 90177536 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x33f2a5cd Device Boot Start End Sectors Size Id Type /dev/vda1 * 2048 2099199 2097152 1G 83 Linux /dev/vda2 2099200 90177535 88078336 42G 83 Linux Command (m for help): w The partition table has been altered. Syncing disks.
Another look at the disks.
nextcloud :: ~ » lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sr0 11:0 1 1024M 0 rom vda 252:0 0 43G 0 disk ├─vda1 252:1 0 1G 0 part /boot └─vda2 252:2 0 42G 0 part ├─cl_nextcloud-root 253:0 0 37G 0 lvm / └─cl_nextcloud-swap 253:1 0 2G 0 lvm
Ok, now we can inform LVM about the new size.
nextcloud :: ~ » sudo pvresize /dev/sda2 Physical volume "/dev/vda2" changed 1 physical volume(s) resized or updated / 0 physical volume(s) not resized nextcloud :: ~ » sudo pvs PV VG Fmt Attr PSize PFree /dev/vda2 cl_nextcloud lvm2 a-- <42.00g 3.00g
Just a few steps left. Resize the logical volume and the filesystem.
Resizing the LV
We should check the logical volumes first.
nextcloud :: ~ » sudo lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert root cl_nextcloud -wi-ao---- <37.00g swap cl_nextcloud -wi-a----- 2.00g
Extend the logical volume “root”. The parameter “-l +100%FREE” grows the logical volume to the maximum limit of the volume group.
nextcloud :: ~ » sudo lvextend -l+100%FREE cl_nextcloud/root Size of logical volume cl_nextcloud/root changed from <37.00 GiB (9471 extents) to <40.00 GiB (10239 extents). Logical volume cl_nextcloud/root successfully resized.
Checking the logical volumes.
nextcloud :: ~ » sudo lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert root cl_nextcloud -wi-ao---- <40.00g swap cl_nextcloud -wi-a----- 2.00g
Resizing the filesystem
Ok, the last step. We need to resize the filesystem to actually use the free space. First, we need to check the filesystem we are using.
nextcloud :: ~ » lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT NAME SIZE TYPE FSTYPE MOUNTPOINT sr0 1024M rom vda 43G disk ├─vda1 1G part ext4 /boot └─vda2 42G part LVM2_member ├─cl_nextcloud-root 40G lvm xfs / └─cl_nextcloud-swap 2G lvm swap
I am using xfs for the root partition. Now to resizing it.
nextcloud :: ~ » sudo xfs_growfs /
meta-data=/dev/mapper/cl_nextcloud-root isize=512 agcount=9, agsize=1113856 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=1
data = bsize=4096 blocks=9698304, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 9698304 to 10484736
That’s it. We grew the virtual machine without any downtime.
Here is a list of the commands without the fluff.
Short list
// KVM Host kvm-router :: ~ » sudo lvextend -L +3G /dev/VM/nextcloud kvm-router :: ~ » sudo blockresize --domain nextcloud --path /dev/VM/nextcloud --size +3G // Virtual Machine nextcloud :: ~ » sudo fdisk /dev/vda Delete and recreate the partition nextcloud :: ~ » sudo pvresize /dev/sda2 nextcloud :: ~ » sudo lvextend -l+100%FREE cl_nextcloud/root nextcloud :: ~ » sudo xfs_growfs /