Hi,
I would like to revisit this old thread from 2016 with a special use
case that I believe should be a standard `virsh` command:
https://lists.gnu.org/archive/html/qemu-devel/2016-12/msg03571.html
**Summary:**
Given this QEMU backing chain:
`base <- snap1 <- snap2 <- snap3 (active)`
We want to merge `base <- snap1 <- snap2` into a new snapshot
`collapsed-base` that is:
1. Sparsified (`virt-sparsify`)
2. Compressed
The resulting backing chain would be:
`collapsed-base <- snap3 (active)`
**Motivation:**
- We perform daily backup snapshots and never modify existing files (too
dangerous). We only rebase.
- We collapse older chains into a new `collapsed-base` snapshot to limit
chain size and avoid performance degradation.
We have been doing this successfully for over 10 years using:
- `qemu-img convert`
- `virt-sparsify`
- `virsh save`
- `qemu-img rebase`
- `virsh resume`
**Problems:**
- There is a small downtime due to `virsh save`/`resume`.
- In recent QEMU versions, `virsh` adds a `backingStore` tag to the XML
even when using the `--no-metadata` option. This causes inconsistencies
after `qemu-img rebase`.
We didn’t use QMP because it didn’t support sparsify + compression in
the past.
**Questions:**
- Is there now a better way to achieve this?
- Could this feature be implemented or supported directly in `virsh`?
In my opinion, this would be the ideal backup solution: we could travel
in time, sync immutable snapshots to a remote backup server, and
maintain performance.
