I would like to use BTRFS to host VMs in VirtualBox to be able to use Snapshots without LVM or such. In theory I don't need
CoW behaviour all the time because of performance reasons and using
nodatacow it seems I don't need to. What I would like to have instead is an approach from my understanding Windows and NTFS seems to be using: Data is changed all the time without
CoW, but if one creates a file system snapshot the current data is kept save within that snapshot by copying data away if it is to be changed in any way. The important thing seems to be that this only happens exactly one time per snapshot and really only for the modified blocks. So after a block to be modified has been copied away at first, all subsequent modifications to the same block are just applied, again without
Besides copying the original block of changed data to some safe place, from a performance perspective this makes a lot of sense to me and I would like to have exactly that behaviour to host my VMs. Those write some data all the time and I simply don't see how I need
CoW behaviour for all those changes.
I only want
CoW after I created a file system snapshot by purpose, e.g. for backup purposes. Afterwards I need
CoW of course to be able to keep my snapshots consistent as long as I need it. But again, even after creation of the snapshots I wouldn't need
CoWfor all eternity for all data, but only once for the afterwards changed blocks. All changes after the first one could simply be applied as without any
From my understanding of the BTRFS docs, if
CoW happens once to some file, it keeps happening forever. But I might be wrong of course...
So, is what I would like to have possible at all with BTRFS?