ZFS and btrfs are not log structured, but CoW. There are some aspects of ZFS like ZIL and L2ARC that are essentially log structured, but the filesystem itself i

ZFS and btrfs are not log structured, but CoW. There are some aspects of ZFS like ZIL and L2ARC that are essentially log structured, but the filesystem itself is not a log structured filesystem. Using CoW in storage is an idea that occurred after in-place and log structured filesystems had been made as far as I know though.