Complete guide to extend guest disk from backend, LVM and Filesystem inside KVM guest.

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First of all this is my guest system layout. There is a disk called ‘vda’ where my guest filesystem resides.


IN GUEST

[root@localhost ~]# fdisk -l

Disk /dev/vda: 6442 MB, 6442450944 bytes, 12582912 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: 0x000b31c1

Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 12582911 5778432 8e Linux LVM

Disk /dev/mapper/fedora-swap: 4227 MB, 4227858432 bytes, 8257536 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 /dev/mapper/fedora-root: 1686 MB, 1686110208 bytes, 3293184 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

Two guest logical volumes ‘fedora-swap’ and ‘fedora-root’ are created inside guest physical volume vda. Discard ‘fedora-swap’ for now.

The physical volume layout is shown below:

[root@localhost ~]# pvs PV VG Fmt Attr PSize PFree /dev/vda2 fedora lvm2 a– 5.51g 0

Now guest image is on a file in host filesystem called ‘nested-guest-f18’.

If your guest system is on a Logical Volume in your host system please refer this article

If I check ‘qemu-img’ information on this guest disk file, I can see

in HOST

[root@humbles-lap vmimgs]# qemu-img info nested-guest-f18.qcow2 image: nested-guest-f18.qcow2 file format: qcow2 virtual size: 6.0G (6442450944 bytes) disk size: 1.5G cluster_size: 65536

So, virtual size is “6.0” G and its a sparse file.

Let me resize the size from qemu-img resize command

[root@humbles-lap vmimgs]# qemu-img resize nested-guest-f18.qcow2 +8G

Image resized.

Check it now:

[root@humbles-lap vmimgs]# qemu-img info nested-guest-f18.qcow2 image: nested-guest-f18.qcow2 file format: qcow2 virtual size: 14G (15032385536 bytes) disk size: 1.5G cluster_size: 65536 [root@humbles-lap vmimgs]#

Looks good.

Now, the changes have been reflected inside guest as you can see in fdisk output..

[root@localhost ~]# fdisk -l

Disk /dev/vda: 15.0 GB, 15032385536 bytes, 29360128 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: 0x000b31c1

Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 12582911 5778432 8e Linux LVM

Disk /dev/mapper/fedora-swap: 4227 MB, 4227858432 bytes, 8257536 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 /dev/mapper/fedora-root: 1686 MB, 1686110208 bytes, 3293184 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

How-ever LVM layout looks same :

[root@localhost ~]# pvs PV VG Fmt Attr PSize PFree /dev/vda2 fedora lvm2 a– 5.51g 0 [root@localhost ~]#

[root@localhost ~]# vgs VG #PV #LV #SN Attr VSize VFree fedora 1 2 0 wz–n- 5.51g 0

[root@localhost ~]# lvs LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert root fedora -wi-ao— 1.57g swap fedora -wi-ao— 3.94g [root@localhost ~]#

Now, lets create a new partition on vda called vda3.

[root@localhost ~]# fdisk /dev/vda Welcome to fdisk (util-linux 2.22.1).

Changes will remain in memory only, until you decide to write them. Be careful before using the write command.

Command (m for help): n Partition type: p primary (2 primary, 0 extended, 2 free) e extended Select (default p): e Partition number (1-4, default 3): Using default value 3 First sector (12582912-29360127, default 12582912): Using default value 12582912 Last sector, +sectors or +size{K,M,G} (12582912-29360127, default 29360127): Using default value 29360127 Partition 3 of type Extended and of size 8 GiB is set

Command (m for help): wq 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. [root@localhost ~]#

Disk /dev/vda: 15.0 GB, 15032385536 bytes, 29360128 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: 0x000b31c1

Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 12582911 5778432 8e Linux LVM /dev/vda3 12582912 29360127 8388608 5 Extended

Disk /dev/mapper/fedora-swap: 4227 MB, 4227858432 bytes, 8257536 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 /dev/mapper/fedora-root: 1686 MB, 1686110208 bytes, 3293184 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

Let me toggle the partition type to LVM :

[root@localhost ~]#fdisk /dev/vda Partition 3 of type Linux and of size 8 GiB is set

Command (m for help): t Partition number (1-4): 3 Hex code (type L to list codes): 8e Changed system type of partition 3 to 8e (Linux LVM)

Command (m for help):

Disk identifier: 0x000b31c1

Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 12582911 5778432 8e Linux LVM /dev/vda3 12582912 29360127 8388608 8e Linux LVM

Disk /dev/mapper/fedora-swap: 4227 MB, 4227858432 bytes, 8257536 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 /dev/mapper/fedora-root: 1686 MB, 1686110208 bytes, 3293184 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

Once its done, let us create a PV on vda3

[root@localhost ~]# pvcreate /dev/vda3 Physical volume “/dev/vda3” successfully created [root@localhost ~]#

[root@localhost ~]# pvs PV VG Fmt Attr PSize PFree /dev/vda2 fedora lvm2 a– 5.51g 0 /dev/vda3 lvm2 a– 8.00g 8.00g

Its the turn to extend the fedora volume group..

[root@localhost ~]# vgextend fedora /dev/vda3 Volume group “fedora” successfully extended [root@localhost ~]#

Now let us extend the logical volume called ‘root’ :

[root@localhost ~]# lvextend -L +6G /dev/fedora/root Extending logical volume root to 7.57 GiB Logical volume root successfully resized [root@localhost ~]#

Once the underlying LVM has enough space, let us try to increase the ext filesystem online..

[root@localhost ~]# resize2fs /dev/fedora/root resize2fs 1.42.5 (29-Jul-2012) Filesystem at /dev/fedora/root is mounted on /; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 1 The filesystem on /dev/fedora/root is now 1984512 blocks long.

[root@localhost ~]#

Disk /dev/vda: 15.0 GB, 15032385536 bytes, 29360128 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: 0x000b31c1

Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 12582911 5778432 8e Linux LVM /dev/vda3 12582912 29360127 8388608 8e Linux LVM

Disk /dev/mapper/fedora-swap: 4227 MB, 4227858432 bytes, 8257536 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 /dev/mapper/fedora-root: 8128 MB, 8128561152 bytes, 15876096 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

[root@localhost ~]#

LVM layer lists the new layout with an increased space of logical volumes.

[root@localhost ~]# pvs PV VG Fmt Attr PSize PFree /dev/vda2 fedora lvm2 a– 5.51g 0 /dev/vda3 fedora lvm2 a– 8.00g 2.00g [root@localhost ~]# vgs VG #PV #LV #SN Attr VSize VFree fedora 2 2 0 wz–n- 13.50g 2.00g [root@localhost ~]# lvs LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert root fedora -wi-ao— 7.57g swap fedora -wi-ao— 3.94g [root@localhost ~]#

All good? if you have any doubts, please feel free to ask in the comments section.

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  1. Pingback: Is it possible to do online resizing of guest block devices ( Or without shutdown ?) » My Humble abode

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