Bug 1519002

Summary: RFE: libvirt - improve support for external snapshots (merge, delete, virsh, etc)
Product: Red Hat Enterprise Linux 9 Reporter: Ademar Reis <areis>
Component: libvirtAssignee: Pavel Hrdina <phrdina>
libvirt sub component: Storage QA Contact: Han Han <hhan>
Status: CLOSED MIGRATED Docs Contact:
Severity: high    
Priority: high CC: accounts+fedora, ailan, aliang, andrew, briasmit, coli, dyuan, eblake, germano, gveitmic, hhan, jsuchane, jwatt, knoel, lersek, libvirt-maint, lmen, luizluca, marcandre.lureau, me, mike, mwest, phrdina, pkrempa, pmores, rm, shipatil, skobyda, smitterl, timao, virt-maint, xuzhang, yafu, ymankad
Version: 9.0Keywords: FutureFeature, MigratedToJIRA, Triaged
Target Milestone: beta   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Enhancement
Doc Text:
Story Points: ---
Clone Of: 1402581 Environment:
Last Closed: 2023-09-22 17:51:33 UTC Type: Story
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version: 9.7.0
Embargoed:
Bug Depends On: 1402581, 1519001, 2170826, 2173142, 2174397, 2174700    
Bug Blocks: 1214187, 1342543, 1403951, 1431852, 1621944, 1997885, 2132850    

Description Ademar Reis 2017-11-29 22:43:31 UTC 
+++ This bug was initially created as a clone of Bug #1402581 +++

Description of problem:
For historical reasons, 'virsh snapshot-create' defaults to internal snapshots, because external snapshots were not implemented for several years.  However, these days the qemu team recommends the use of external snapshots, and upper levels like RHEV prefer external snapshots.  It would be nice if there were a way to set up configuration defaults for virsh, so that typing 'virsh snapshot-create' could consult the configuration file on whether to default to internal or external, instead of forcing the user to remember to pass extra flags to get an external snapshot.

Version-Release number of selected component (if applicable):
libvirt-2.5.0-1.el7

How reproducible:
100%

Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info:


--- Additional comment from Laszlo Ersek on 2017-02-24 20:50:15 BRT ---

When designing this feature for virsh (and virt-manager), please don't forget about the UEFI varstore files (under /var/lib/libvirt/qemu/nvram), which are technically raw drives, but have very different storage properties from normal drives. They don't live in storage pools, they are not on shared storage, and also not subject to storage migration. QEMU automatically writes them out fully on the target host after migration finishes.

I'm unsure how this interacts with external snapshots, but I figure I'd better raise it. Thanks.
Comment 5 Peter Krempa 2020-06-30 20:05:46 UTC 
There are multiple options how to create an external snapshot:

1) using virsh snapshot-create-as (see man page for further explanation):

1.1) if the VM is active, but the user doesn't want to take a snapshot of the memory

  virsh snapshot-create-as $VMNAME --disk-only

1.2) if the vm is active and memory snapshot is required
 
  virsh snapshot-create-as $VMNAME --memspec file=/path/to/memory-image,snapshot=external

1.3) if disks which take part of the snapshot need to be controlled:

  virsh snapshot-create-as $VMNAME --memspec file=/path/to/memory-image,snapshot=external --diskspec vda,snapshot=no --diskspec vdb,file=/path/to/overlay-img

1.4) any additional options such as snapshot name, description etc can be controlled using additional parameters. Please refer to the man page:

https://libvirt.org/manpages/virsh.html#snapshot-create-as

2) using virsh snapshot create

This option requires an XML document describing the snapshot as argument. Please refer to the documentation.

For inspiration, a sample XML can be obtained using the '--print-xml' argument for 'virsh snapshot-create-as' which prints the XML the command generates.

snapshot XML documentation:

https://libvirt.org/formatsnapshot.html

Please note, that while creating external snapshots works, we don't yet have implementation for reverting or deleting external snapshots, thus internal snapshots must be supported until then.

Regarding customer's question, rhel-7.6 already supports external snapshots to the extent above.

If required there are manual steps which allow reversion or deletion of external snapshots.
Comment 29 RHEL Program Management 2023-09-22 17:50:43 UTC 
Issue migration from Bugzilla to Jira is in process at this time. This will be the last message in Jira copied from the Bugzilla bug.
Comment 30 RHEL Program Management 2023-09-22 17:51:33 UTC 
This BZ has been automatically migrated to the issues.redhat.com Red Hat Issue Tracker. All future work related to this report will be managed there.

Due to differences in account names between systems, some fields were not replicated.  Be sure to add yourself to Jira issue's "Watchers" field to continue receiving updates and add others to the "Need Info From" field to continue requesting information.

To find the migrated issue, look in the "Links" section for a direct link to the new issue location. The issue key will have an icon of 2 footprints next to it, and begin with "RHEL-" followed by an integer.  You can also find this issue by visiting https://issues.redhat.com/issues/?jql= and searching the "Bugzilla Bug" field for this BZ's number, e.g. a search like:

"Bugzilla Bug" = 1234567

In the event you have trouble locating or viewing this issue, you can file an issue by sending mail to rh-issues. You can also visit https://access.redhat.com/articles/7032570 for general account information.