Scenario: I am running several virtual machine guests using
QEMU/KVM.
Both the host and guest operating systems are Ubuntu 12.04 LTS. The
guests are raw images (as opposed to QEMU qcow2 or disk partitions). My
instructions for setting up the virtual machines are
here. One of the guests image is stored on the host as:
sgordon@host:~$ ls -lhs /var/vm/
total 14G
14G -rwxr-xr-x 1 libvirt-qemu kvm 20G May 18 14:26 it.img
Currently the image is allocated 20GB of space. But note that as Linux
ext4 file systems support sparse files, it only takes up 14GB on the
disk, as the guest is only using 14GB of the 20GB space available. (The
-s option for
ls shows the actual size). In the guest virtual machine I am using LVM and ext4 filesystems.
My goal is to increase the size of the guests hard disk, i.e. increase
the raw image size. In this case I will increase it from 20GB to 45GB.
Mathew Branwell
gives a detailed description of the steps involved. I've basically
copied his instructions, with some minor changes to resizing the guest
image. In summary the steps are:
- On the host: Increase the size of the guests image
- On the guest: Increase the disk partition
- On the guest: Increase the LVM physical and logical volumes
- On the guest: Increase the file system size
Note that these steps only apply for
increasing the size. Decreasing the size is a bit different and has greater potential of data loss.
Guest: Shutdown the Guest Virtual Machine
Before getting started, lets just summarise some details about the
guest, in particular the LVM Physical Volumes, Logical Volumes and
filesystems. Note that in the examples
guest is shown in the prompt indicating the commands are run in the guest (as opposed to the
host).
sgordon@guest:~$ sudo pvs
PV VG Fmt Attr PSize PFree
/dev/vda5 vmit lvm2 a- 19.81g 0
sgordon@guest:~$ sudo lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
home vmit -wi-ao 5.84g
root vmit -wi-ao 4.66g
tmp vmit -wi-ao 4.66g
var vmit -wi-ao 4.66g
sgordon@guest:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vmit-root 4.7G 1.8G 2.7G 40% /
udev 728M 4.0K 728M 1% /dev
tmpfs 293M 264K 293M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 732M 0 732M 0% /run/shm
/dev/vda1 189M 24M 155M 14% /boot
/dev/mapper/vmit-tmp 4.7G 198M 4.3G 5% /tmp
/dev/mapper/vmit-var 4.7G 1.3G 3.2G 28% /var
/dev/mapper/vmit-home 5.9G 2.5G 3.1G 45% /home
The first step is to shutdown the guest virtual machine:
sgordon@guest:~$ sudo shutdown -P now
Broadcast message from sgordon@guest
(/dev/pts/0) at 14:51 ...
The system is going down for power off NOW!
Host: Increase the Virtual Machine Image Size
Now resize the image on the host machine:
sgordon@host:~$ sudo qemu-img resize /var/vm/guest.img +25G
Image resized.
This increases the guest image file by 25GB. To check:
sgordon@host:~$ ls -lhs /var/vm/
total 14G
14G -rwxr-xr-x 1 root root 45G May 18 14:53 guest.img
Now start and login to the guest for the remaining steps:
sgordon@host$ sudo virsh start guest
Domain it started
sgordon@host$ ssh guest
Guest: Increase the Partition Size
First on the guest we need to increase the partition sizes using
fdisk:
sgordon@guest:~$ sudo fdisk /dev/vda
Command (m for help):
fdisk takes single letter commands as described in the help. Using the command
p to print the current partitions:
Command (m for help): p
Disk /dev/vda: 48.3 GB, 48318382080 bytes
16 heads, 63 sectors/track, 93622 cylinders, total 94371840 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
Disk identifier: 0x00079e72
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 391167 194560 83 Linux
/dev/vda2 393214 41940991 20773889 5 Extended
/dev/vda5 393216 41940991 20773888 8e Linux LVM
Note that my disk (
/dev/vda) is 48.3GB, but my partitions are only using 20GB (20773888 blocks).
Be careful! Your partitions will be different from
mine. Use the devices/sizes for your partitions in the following
examples. I have an initial
boot partion on
/dev/vda1 followed by an extended partition with Linux LVM.
I want to increase the size of the Extended and Linux LVM partitions by
first deleting them and then creating new ones of the same type but
different size. Note the device names and system/IDs in your partition
table.
To delete partitions use the
d command and specifiy the partition number (2 and 5 in my case):
Command (m for help): d
Partition number (1-5): 5
Command (m for help): d
Partition number (1-5): 2
Command (m for help): p
Disk /dev/vda: 48.3 GB, 48318382080 bytes
16 heads, 63 sectors/track, 93622 cylinders, total 94371840 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
Disk identifier: 0x00079e72
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 391167 194560 83 Linux
Now lets create new partitions. I will use the same structure as before but use the entire disk. Use the
n command:
Command (m for help): n
Partition type:
p primary (1 primary, 0 extended, 3 free)
e extended
Select (default p): e
Partition number (1-4, default 2): 2
First sector (391168-94371839, default 391168): <ENTER>
Using default value 391168
Last sector, +sectors or +size{K,M,G} (391168-94371839, default 94371839): <ENTER>
Using default value 94371839
I create a new extended partition number 2 using the default first and
last sectors. I also need to create the second new logical partition:
Command (m for help): n
Partition type:
p primary (1 primary, 1 extended, 2 free)
l logical (numbered from 5)
Select (default p): l
Adding logical partition 5
First sector (393216-94371839, default 393216): <ENTER>
Using default value 393216
Last sector, +sectors or +size{K,M,G} (393216-94371839, default 94371839): <ENTER>
Using default value 94371839
I also need to specify the type of the logical partition, i.e. Linux
LVM. From the original partition table the Id of the Linux LVM system is
8e:
Command (m for help): t
Partition number (1-5): 5
Hex code (type L to list codes): 8e
Changed system type of partition 5 to 8e (Linux LVM)
The resulting partition table follows. Note that is is the same
structure as the original table but the size of the last two partitions (
/dev/vda2 and
/dev/vda5) have changed from 20GB to about 45GB.
Command (m for help): p
Disk /dev/vda: 48.3 GB, 48318382080 bytes
16 heads, 63 sectors/track, 93622 cylinders, total 94371840 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
Disk identifier: 0x00079e72
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 391167 194560 83 Linux
/dev/vda2 391168 94371839 46990336 5 Extended
/dev/vda5 393216 94371839 46989312 8e Linux LVM
If your partition table is correct then the last step is to write those changes:
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
sgordon@guest:~$
Note the warning: you need to reboot for the new partition table to be read:
sgordon@guest:~$ sudo shutdown -r now
Broadcast message from sgordon@it
(/dev/pts/0) at 15:15 ...
The system is going down for reboot NOW!
Guest: Increase the LVM Physical and Logical Volume Sizes
Note that this step only applies if you are using LVM.
After rebooting and logging back in, we need to update LVM. First note
the current size of the Physical Volume. On my guest virtual machine I
have one physical volume:
sgordon@guest:~$ sudo pvs
PV VG Fmt Attr PSize PFree
/dev/vda5 vmit lvm2 a- 19.81g 0
We need to resize the physical volume:
sgordon@guest:~$ sudo pvresize /dev/vda5
Physical volume "/dev/vda5" changed
1 physical volume(s) resized / 0 physical volume(s) not resized
sgordon@guest:~$ sudo pvs
PV VG Fmt Attr PSize PFree
/dev/vda5 vmit lvm2 a- 44.81g 25.00g
The physical volume now takes the full space of 45GB, and there is 25GB
free. We will extend the Logical Volumes to use that extra 25GB. In my
case I have four logical volumes:
home,
root,
tmp and
var (and the correpending directories are mount to them). In this case I want to increase the size of the
home and
var volumes by 15GB and 10GB, respectively. I will use
lvextend which requires you to specify the logical volume relative to the volume group.
sgordon@guest:~$ sudo vgs
VG #PV #LV #SN Attr VSize VFree
vmit 1 4 0 wz--n- 44.81g 25.00g
The name of my volume group is
vmit. So now lets extend the two logical volumes:
sgordon@guest:~$ sudo lvextend -L +15G /dev/vmit/home
Extending logical volume home to 20.84 GiB
Logical volume home successfully resized
sgordon@guest:~$ sudo lvextend -L +10G /dev/vmit/var
Extending logical volume var to 14.66 GiB
Logical volume var successfully resized
The result, as shown below, is the volume group now has no space free and the
home>/kbd> and var logical volumes are now 21GB and 15GB, respectively.
sgordon@guest:~$ sudo vgs
VG #PV #LV #SN Attr VSize VFree
vmit 1 4 0 wz--n- 44.81g 0
sgordon@guest:~$ sudo lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
home vmit -wi-ao 20.84g
root vmit -wi-ao 4.66g
tmp vmit -wi-ao 4.66g
var vmit -wi-ao 14.66g
Guest: Increase the Filesystem Sizes
The last step is to grow the filesystems to use the entire logical
volume. Currently the filesystems sizes are still the original sizes, as
shown below.
sgordon@guest:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vmit-root 4.7G 1.8G 2.7G 40% /
udev 728M 4.0K 728M 1% /dev
tmpfs 293M 252K 293M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 732M 0 732M 0% /run/shm
/dev/vda1 189M 24M 155M 14% /boot
/dev/mapper/vmit-tmp 4.7G 198M 4.3G 5% /tmp
/dev/mapper/vmit-var 4.7G 1.3G 3.2G 28% /var
/dev/mapper/vmit-home 5.9G 2.5G 3.1G 45% /home
In my case I am using ext4 filesystems and using
resize2fs I
can increase their size online, that is, while they're mounted. If you
have a different filesystem (or possibly older kernel) online resizing
may not be possible; you may need to unmount the filesystems first.
sgordon@guest:~$ sudo resize2fs /dev/vmit/home
resize2fs 1.42 (29-Nov-2011)
Filesystem at /dev/vmit/home is mounted on /home; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/vmit/home to 5463040 (4k) blocks.
The filesystem on /dev/vmit/home is now 5463040 blocks long.
sgordon@guest:~$ sudo resize2fs /dev/vmit/var
resize2fs 1.42 (29-Nov-2011)
Filesystem at /dev/vmit/var is mounted on /var; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/vmit/var to 3842048 (4k) blocks.
The filesystem on /dev/vmit/var is now 3842048 blocks long.
Note that the resize takes some time. Finally, check the new sizes:
sgordon@guest:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vmit-root 4.7G 1.8G 2.7G 40% /
udev 728M 4.0K 728M 1% /dev
tmpfs 293M 252K 293M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 732M 0 732M 0% /run/shm
/dev/vda1 189M 24M 155M 14% /boot
/dev/mapper/vmit-tmp 4.7G 198M 4.3G 5% /tmp
/dev/mapper/vmit-var 15G 1.3G 13G 9% /var
/dev/mapper/vmit-home 21G 2.5G 18G 13% /home
I now have a 15GB
/var filesystem and a 21GB
/home filesystem.
Source:
https://sandilands.info/sgordon/increasing-kvm-virtual-machine-disk-using-lvm-ext4
