It depends of would do you with BTRFS. We are using on our small-scale servers where we have many small VM (20~40GiB) that have BTRFS as root with transparent

It depends of would do you with BTRFS. We are using on our small-scale servers where we have many small VM (20~40GiB) that have BTRFS as root with transparent compression. It make more easy expand a VM hard disk, as we only need to add a new virtual hard disk and add it to the BTRFS. Some of our VM's are on HyperV and this means stoping the VM to add a new hard disk or resize the virtual hd. Other are on a new server running Proxmox that allows add virtual hard disk without stoping the VM, that allow us to add extra hard disk space with stoping the VM server. I only need to schedule a weekly rebalance of the BTRFS (Ubuntu server 16.04 don't does this!) and I have a script to check free space and available chunks on the FS to avoid any problem with a full BTRFS partition. I remember having a issue with BTRFS two years ago when go a unexpected powerdown (the SAI don't help us as was a short-circuit after the SAI!) where a HyperV VM with BTRFS had the FS corrupted, but we managed to recover the data. Also we have a physical server to run Jenkins and GitLab that it's using FakeRaid + BTRFS + btrbk to schedule backups using snapshots and btrfs send, that are stored as compressed files on a network folder (and this folder are backuped to magnetic tapes). I don't noticed any slowdown when I launched a manual rebalance, but we are operating at low scale so we not have a lot of I/O. Our real bottleneck are the databases that are on Windows servers.