Adding cc:s. Christopher Pereira <kripper@imatronix.cl> writes:
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.