What is the impact if I backup the drives of running KVM

[Lacey_Chu]

Hi Experts,

I have one linux red hat client v7.7 and there is /var/images/hpg82 which is used to save the related files of my KVM.

I want to know the detailed impact if I do standard backup with /var/images/hpg82 while the VM is running.

[root@xun bin]# virsh list --all
 Id    Name                           State
----------------------------------------------------
 4     hpg82                          running

[root@xun bin]# cd /var/images/hpg82
[root@xun hpg82]# ll
total 6305536
-rw-------. 1 root root     376832 Sep  7 16:17 configdrive.iso
-rw-------. 1 root root     200704 Sep  7 16:18 datadisk.qcow2
-rw-------. 1 root root 6456344576 Sep  7 16:18 rhel.qcow2
-rw-------. 1 root root       2845 Sep  7 16:17 vmdomain.xml
[root@xun hpg82]#

Regards,

Lacey

[Nicolai · Accepted solution]

The data inside the KVM VM will be in-consistent.

If the VM is idle it may just work, but on a highly busy system expect to have a lot of maybe un-repairable file system inconsistencies.

Only way to ensure data is 100% valid is to stop the VM during backup.

Alternative - investigate if KVM has snapshot functationality. Found this - says QEMU - don't know if this is the same as KVM

[Michael_G_Ander]

Don't know KVM, but assume that you need to make a snapshot of the VM and take backup of that or install a client inside the VM to have a consistent backup . That is the options on other virtualization systems like VMWARE and Hyper-V.

[Lacey_Chu]

Do you mean that Symantec NetBackup uses QEMU command to backup *.qcow2 files?

[Marianne]

NetBackup does not have an agent for KVM. This means you cannot take backups at hypervisor level while VMs are online. You need to install NBU client in each VM and take backup same as physical client or shutdown VMs to take backups of *.qcow2.