Ok, I have a simple question. I have a modern server and I want to
make advanced configuration for my TB data (eg. hard drives hot
swapping etc.), so I'm doing something like this:

dd if=/dev/zero of=/dev/sda bs=4096

mkfs.btrfs -L dev_sda /dev/sda
mount /dev/sda /mnt

cd /mnt
btrfs subvolume create __active
btrfs subvolume create __active/rootvol
btrfs subvolume create __active/usr
btrfs subvolume create __active/home
btrfs subvolume create __active/var
btrfs subvolume create __snapshots

cd /
umount /mnt
mount -o subvol=__active/rootvol /dev/sda /mnt
mkdir /mnt/{usr,home,var}
mount -o subvol=__active/usr /dev/sda /mnt/usr
mount -o subvol=__active/home /dev/sda /mnt/home
mount -o subvol=__active/var /dev/sda /mnt/var

(Linux installation...)

# /etc/fstab
UUID=ID    /    btrfs rw,relative,space_cache,subvol=__active/rootvol    0 0
UUID=ID    /usr    btrfs rw,relative,space_cache,subvol=__active/usr    0 0
UUID=ID    /home    btrfs rw,relative,space_cache,subvol=__active/home    0 0
UUID=ID    /var    btrfs rw,relative,space_cache,subvol=__active/var    0 0

No partitions (MBR or GPT), everything is running on btrfs. It's easy
to add new disks.

And now the question is: which bootloader supports something like that?

* lilo - no, it does not support.
* grub 0.97 - no, it does not support.
* grub 2 - yes, it works (I confirm).
* extlinux - probably works, but not tested.

I have no problem to accept lilo, but I want to be able to use
advanced configuration.

Daniel