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Linux KVM – How to Add/Resize Virtual disk on fly? Part 7

In this article ,we will see that how to add new virtual disk or LUN to the KVM guest and how to resize the existing virtual disk on active domain/guest. This operations can be carried out on fly without any downtime to the guest operating system. KVM supports both physical LUN mapping and virtual disk mapping to the guests. In an order to map the virtual disk , we need to create the virtual disk image file using qemu-img command and disk format can be either “img” or “qcow2”.  You  can also create the non-sparse image file using legacy “dd” command.

Environment:  RHEL 7  KVM Hypervisor

 

Mapping SAN or SCSI Disks to the KVM Guests:

1.Login to the KVM hypervisor host as root user.

2. Assume that we got “/dev/sdb” LUN from SAN storage to the hypervisor node.

3.List the running virtual machine using virsh command.

[root@UA-HA ~]# virsh list
 Id    Name                           State
----------------------------------------------------
 32    UAKVM2                         running
[root@UA-HA ~]#

 

4. Identify the existing device mapping for the UAKVM2 guest.

[root@UA-HA ~]# virsh domblklist UAKVM2 --details
Type       Device     Target     Source
------------------------------------------------
file       disk       vda        /var/lib/libvirt/images/UAKVM2.qcow2
block      cdrom      hda        -
[root@UA-HA ~]#

 

5. Attach the LUN to UAKVM2 virtual KVM guest as vdb device.

[root@UA-HA ~]# virsh attach-disk UAKVM2 --source /dev/sdb --target vdb --persistent
Disk attached successfully
[root@UA-HA ~]#

 

6. verify our work.

[root@UA-HA ~]# virsh domblklist UAKVM2 --details
Type       Device     Target     Source
------------------------------------------------
file       disk       vda        /var/lib/libvirt/images/UAKVM2.qcow2
block      disk       vdb        /dev/sdb
block      cdrom      hda        -
[root@UA-HA ~]#

 

7. Login to UAKVM2 KVM guest and check the newly assigned disk.

[root@UA-KVM1 ~]# fdisk -l /dev/vdb

Disk /dev/vdb: 536 MB, 536870912 bytes, 1048576 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@UA-KVM1 ~]#

We have successfully mapped “/dev/sdb”   SAN LUN to the KVM guest on fly.

 

Add new virtual Disk to the KVM Guests:

To map the virtual disk to KVM host,

  • Create the new virtual disk using qemu-img command.
  • Attach the virtual disk to the guest domain.

 

1. Login to UAKVM2 and list the attached disks.

[root@UA-KVM1 ~]# fdisk -l |grep vd |grep -v Linux
Disk /dev/vda: 4294 MB, 4294967296 bytes, 8388608 sectors
Disk /dev/vdb: 536 MB, 536870912 bytes, 1048576 sectors
[root@UA-KVM1 ~]#

 

2. Login to the KVM hypervisor .

 

3. Create new virtual disk using qemu-img command.

[root@UA-HA images]# cd /var/lib/libvirt/images
[root@UA-HA images]# qemu-img create -f qcow2 UAKVM2.disk2.qcow2 1G
Formatting 'UAKVM2.disk2.qcow2', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off
[root@UA-HA images]#

Note: Storage pool path will not be same on all the environments.

You can also create the virtual disks in following methods.

  • Raw format with thin provisioning:
[root@UA-HA images]# qemu-img create -f raw UAKVM2.disk3.img 256M
Formatting 'UAKVM2.disk3.img', fmt=raw size=268435456
[root@UA-HA images]#
  • Raw format with thick provisioning: (Provides Better Performance since it’s pre-allocated storage)
[root@UA-HA images]# dd if=/dev/zero of=UAKVM2.disk4.img bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 14.6078 s, 71.8 MB/s
[root@UA-HA images]#

 

See the virtual disk size in the storage pool.

[root@UA-HA images]# du -sh UAKVM2.disk*
196K    UAKVM2.disk2.qcow2      --- qcow2 formatted virtual disk file (thin)
0       UAKVM2.disk3.img        --- raw  formatted virtual disk file (thin)
1000M   UAKVM2.disk4.img        --- raw  formatted virtual disk file using dd command. 
[root@UA-HA images]#

 

4. Attach the virtual disk to the KVM guest.

[root@UA-HA images]# virsh attach-disk UAKVM2 --source /var/lib/libvirt/images/UAKVM2.disk2.qcow2 --target vdc --persistent
Disk attached successfully
[root@UA-HA images]#

 

5. Verify our work.

[root@UA-HA images]# virsh domblklist UAKVM2 --details
Type       Device     Target     Source
------------------------------------------------
file       disk       vda        /var/lib/libvirt/images/UAKVM2.qcow2
block      disk       vdb        /dev/sdb
file       disk       vdc        /var/lib/libvirt/images/UAKVM2.disk2.qcow2
block      cdrom      hda        -
[root@UA-HA images]#

 

6. Login to the virtual guest (UAKVM2) and check the newly added disk.

[root@UA-KVM1 ~]# fdisk -l /dev/vdc
Disk /dev/vdc: 1073 MB, 1073741824 bytes, 2097152 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@UA-KVM1 ~]#

We have successfully created the virtual disks and present to the KVM guest on fly.

 

Resize existing virtual Disks on KVM:

1.Login to the Guest VM (UAKVM2) and identify which disk require to resize.

[root@UA-KVM1 ~]# df -h /orastage
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdc       1014M   33M  982M   4% /orastage
[root@UA-KVM1 ~]# mount -v |grep /orastage
/dev/vdc on /orastage type xfs (rw,relatime,attr2,inode64,noquota)
[root@UA-KVM1 ~]#
[root@UA-KVM1 ~]# fdisk -l /dev/vdc

Disk /dev/vdc: 1073 MB, 1073741824 bytes, 2097152 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@UA-KVM1 ~]#

 

2. Login to the KVM hypervisor which hosts the VM

 

3. Identify the virtual disk mapping for the KVM guest.

[root@UA-HA ~]# virsh domblklist UAKVM2 --details
Type       Device     Target     Source
------------------------------------------------
file       disk       vda        /var/lib/libvirt/images/UAKVM2.qcow2
block      disk       vdb        /dev/sdb
file       disk       vdc        /var/lib/libvirt/images/UAKVM2.disk2.qcow2
block      cdrom      hda        -

[root@UA-HA ~]#

 

4. Refresh the KVM storage pool.

[root@UA-HA ~]# virsh pool-list
 Name                 State      Autostart
-------------------------------------------
 default              active     yes
 [root@UA-HA ~]#
[root@UA-HA ~]# virsh pool-refresh default
Pool default refreshed
[root@UA-HA ~]#

 

5. List the virtual disks using virsh-vol list command. (vdc = UAKVM2.disk2.qcow2)

[root@UA-HA ~]# virsh vol-list  default
 Name                 Path
------------------------------------------------------------------------------
 UAKVM2.disk2.qcow2   /var/lib/libvirt/images/UAKVM2.disk2.qcow2
 UAKVM2.disk3.img     /var/lib/libvirt/images/UAKVM2.disk3.img
 UAKVM2.disk4.img     /var/lib/libvirt/images/UAKVM2.disk4.img
 UAKVM2.qcow2         /var/lib/libvirt/images/UAKVM2.qcow2
[root@UA-HA ~]#

 

6. Use “qemu-monitor” to list the allocated block devices to “UAKVM2” domain.

[root@UA-HA ~]# virsh qemu-monitor-command UAKVM2 --hmp "info block"
drive-virtio-disk0: removable=0 io-status=ok file=/var/lib/libvirt/images/UAKVM2.qcow2 ro=0 drv=qcow2 encrypted=0 bps=0 bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0
drive-virtio-disk1: removable=0 io-status=ok file=/dev/sdb ro=0 drv=raw encrypted=0 bps=0 bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0
drive-virtio-disk2: removable=0 io-status=ok file=/var/lib/libvirt/images/UAKVM2.disk2.qcow2 ro=0 drv=raw encrypted=0 bps=0 bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0
drive-ide0-0-0: removable=1 locked=0 tray-open=0 io-status=ok [not inserted]
[root@UA-HA ~]#

From the above command output, we can see that virtual disk “UAKVM2.disk2.qcow2” is mapped to drive-virtio-disk2.

 

7. Increase the virtual disk size and intimate the virtio driver about the changes. (Do not reduce the disk size !!!)

[root@UA-HA images]# virsh qemu-monitor-command UAKVM2 --hmp "block_resize drive-virtio-disk2 2G"
[root@UA-HA images]#

 

8. Login to the KVM guest – UAKVM2 and check the “vdc” disk size.

[root@UA-KVM1 ~]# fdisk -l /dev/vdc

Disk /dev/vdc: 2147 MB, 2147483648 bytes, 4194304 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@UA-KVM1 ~]#

 

9. Extend the filesystem. My filesystem type is XFS.

[root@UA-KVM1 ~]# df -h /orastage
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdc       1014M   33M  982M   4% /orastage
[root@UA-KVM1 ~]# mount -v |grep /orastage
/dev/vdc on /orastage type xfs (rw,relatime,attr2,inode64,noquota)
[root@UA-KVM1 ~]#
[root@UA-KVM1 ~]# xfs_growfs /orastage/
meta-data=/dev/vdc               isize=256    agcount=4, agsize=65536 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=0        finobt=0
data     =                       bsize=4096   blocks=262144, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
log      =internal               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 262144 to 1310720
[root@UA-KVM1 ~]#
[root@UA-KVM1 ~]# df -h /orastage/
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdc        2.0G   33M  2.0G   1% /orastage
[root@UA-KVM1 ~]#

We have successfully resized virtual size and intimated to virtio driver about the changes. No specific instructions required for the VM to see the new disk size.

 

Hope this article informative to you.

VMTURBO-CLOUD-CAPACITY

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