Qemu-img Differences between Snapshots: Difference between revisions
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2. Trigger the event. | 2. Trigger the event. | ||
3. Save the state of the filesystem after the event, by cloning the filesystem, with [[Virsh vol-clone|virsh vol-clone]]: | 3. Save the state of the filesystem after the event, by cloning the filesystem, with [[Virsh vol-clone|virsh vol-clone]], after the VM guest has been shut down: | ||
virsh vol-clone --pool main-storage-pool --prealloc-metadata build-guest.qcow2 build-guest-after.qcow2 | virsh vol-clone --pool main-storage-pool --prealloc-metadata build-guest.qcow2 build-guest-after.qcow2 | ||
4. Revert the original filesystem to the state before the event, by reverting to snapshot, with [[Qemu-img#Revert_the_Disk_to_a_Saved_State|qemu-img snapshot -a <''snapshot-tag''> <''volume-name''>]]. | |||
5. Optionally, delete the snapshot with [[Qemu-img#Delete_the_Snapshot|qemu-img snapshot -d <''snapshot-tag''> <''volume-name''>]]. | |||
6. Display the difference: | |||
[[virt-diff#Procedures|virt-diff]] -a <''image-before''> -A <''image-after''> | |||
[[virt-diff#Procedures|virt-diff]] -a /main-storage-pool/build-guest.qcow2 -A /main-storage-pool/build-guest-after.qcow2 > .../diff.txt | |||
7. Delete the cloned "after" filesystem with [[Virsh_vol-delete#Overview|virsh vol-delete ...]] | |||
Latest revision as of 18:58, 18 December 2017
Internal
Overview
This is a procedure that can be used to list differences between qemu-img snapshots. It is probably not optimal, and there are probably tools that do this better, but at the time of the writing, I did not know about them.
Procedure
1. Take a snapshot of the filesystem before the event whose effects you want to analyze: qemu-img snapshot -c ...
2. Trigger the event.
3. Save the state of the filesystem after the event, by cloning the filesystem, with virsh vol-clone, after the VM guest has been shut down:
virsh vol-clone --pool main-storage-pool --prealloc-metadata build-guest.qcow2 build-guest-after.qcow2
4. Revert the original filesystem to the state before the event, by reverting to snapshot, with qemu-img snapshot -a <snapshot-tag> <volume-name>.
5. Optionally, delete the snapshot with qemu-img snapshot -d <snapshot-tag> <volume-name>.
6. Display the difference:
virt-diff -a <image-before> -A <image-after>
virt-diff -a /main-storage-pool/build-guest.qcow2 -A /main-storage-pool/build-guest-after.qcow2 > .../diff.txt
7. Delete the cloned "after" filesystem with virsh vol-delete ...