Dear KVM Team,
I am currently evaluating different approaches to achieve VM-consistent
snapshots and would appreciate your insights on the matter.
My analysis has identified two main approaches for quiescing a VM:
1. Quiescing by pausing (or suspending) the entire VM - as currently
implemented using the
virsh suspend
This is a disruptive option as it halts the VM's execution.
1. Quiescing by freezing the file system inside the VM - typically performed
via the QEMU guest agent using the
domfsfreeze / domfsthaw
This option is non-disruptive because it allows the VM to
continue running while ensuring file system consistency.
Technically, the second option appears preferable. However, its implementation
hinges on the following considerations:
* The QEMU guest agent must be installed and running within the guest OS.
While this is often the case by default, it may not be present in all Linux
Flavors. Ensuring its availability is therefore a prerequisite.
* In Windows environments, the QEMU guest agent freeze leverages VSS
(Volume Shadow Copy Service), and in Linux, it uses fsfreeze. Since fsfreeze
freezes I/O, I would like to understand if this temporary freeze might impact
user operations. Additionally, are there any alternative mechanisms to achieve
a consistent backup without relying solely on the QEMU guest agent?
Could you please clarify:
* The potential impact on user operations during the fsfreeze operation in
Linux environments.
* Whether there are alternative methods or improvements on the existing
approach to obtain VM-consistent backups without significant disruption or
reliance on the QEMU guest agent.
Thank you for your assistance. I look forward to your valuable feedback.
Best regards,
Raj.
