Local storage root disk is melded with its template

[yadvr]

Tested a few scenarios (not sure exactly which one) but in my testing caused the root of the VM melded to its template when using local storage on KVM;

• VM migration (with local storage) from one host to another
• VM's root disk volume take snapshot & revert to the volume snapshot
• VM's instance snapshot first with disk & revert; next VM snapshot with memory & revert

Expected that VM's root disk in case of root disk still uses the template as backing file.

ISSUE TYPE

• Bug Report

COMPONENT NAME

KVM, local storage VM

CLOUDSTACK VERSION

4.19/4.19.1

CONFIGURATION

Adv zone ubuntu with local storage (22.04)

OS / ENVIRONMENT

Ubuntu 22.04

[DaanHoogland]

@rohityadavcloud , can you update the issue (if you have more precise data), please?

[JoaoJandre]

@rohityadavcloud @DaanHoogland The first behavior was explained in #8911:

Currently, when a volume that was created with linked clone is live migrated from an NFS storage to another NFS storage in KVM, it continues to have the template as a backing file on the destination storage. In all other cases, such as NFS to SharedMountPoint, the volume is consolidated with its backing file during migration.

Migrating from local to local storage would consolidate the volume and its template. However, since #8911 was accepted, this behavior has been changed, now the volume should keep its template on every file-based to file-based storage migration (using KVM).

Regarding your second case, when reverting a volume snapshot, the volume will no longer have a backing file, this is expected from the snapshot process, I don't believe it has ever been different.

About your last case, since the current disk-only VM snapshot process is based on the volume snapshot process, it has the same behavior as above. Once #9270 is accepted, I plan on opening a PR that will introduce a new disk-only VM snapshot process which will keep the volume's backing file (among other benefits).

[yadvr]

Closing this for now.