Am 25.11.2018 um 19:55 hat Nir Soffer geschrieben:
On Fri, Nov 23, 2018 at 1:01 PM Nathanaël Blanchet <blanchet@abes.fr> wrote:
What are the best pratices about vm snapshots?
I think the general guideline is keep only snapshot you need, since every snapshot has a potential performance cost.
qemu caches some image metadata in memory, so accessing data from an image with 20 snapshots should be efficient as image with 2 snapshots, but using more snapshots will consume more memory.
The memory will also only really be used when the backing file is actually accesses. So if you keep very old snapshots, but all data has already been overwritten and the old snapshot is never accessed, it doesn't need that memory. Additionally, starting with QEMU 3.1, cache-clean-interval is active by default and frees the cached table of a snapshot layer when it hasn't been accessed for 10 minutes. (You had to enable it explicitly before that, which I don't think oVirt does.)
Kevin, do we have performance tests comparing VMs with different amount of snapshots?
I'm not aware of a proper performance test where this aspect was tested. Kevin