HOTPLUG_SNAPSHOT takes about 1h after changing cache=writethrough to none

OpenNebula version:5.12.01

i changed the cache mode from writetrough to none, increased the vm memory from 8GB to 16GB on the vm and doubled the size of the swap file.

Before these actions the vm live snapshot (HOTPLUG_SNAPSHOT:create snapshot) took about 3-5 minutes. Now (on NVME SSD Storage !) it takes about 55 minutes to complete.

HOTPLUG_SNAPSHOT:delete snapshot - the time for deletion a snapshot is quite the same (before & after the mentioned changes).

i’m aware of doubling the memory and swap size, increases the time for the live snapshot, because memory information will be dumped into the snapshot.

Is this behave OpenNebula or qemu-img related ? (takes much more time to complete the live snap operation, when cache=none is used)

In this scenario it makes not much sense for me to do a live snapshot … i could also just make an offline backup of vm Disk, which takes - more or less - the same time to complete.

i’m appreciating any input. thx a lot.