Also Synology use btrfs, a copy-on-write filesystem - that means there are operations that you might not expect that require allocation of new blocks - like an

Also Synology use btrfs, a copy-on-write filesystem - that means there are operations that you might not expect that require allocation of new blocks - like any write, even if overwriting an existing file's data. And "unexpected" failure paths like that are often poorly tested in apps.