LVM

#xfs(stable):

pvcreate /dev/md4
vgcreate SLOW /dev/md4
lvcreate -n backup -L5T SLOW
mkfs.xfs /dev/SLOW/backup

mkdir -p /backup; mount /dev/SLOW/backup /backup

lvextend -L+1T /dev/SLOW/backup
xfs_growfs -d /backup

#reiserfs (old good):

resize_reiserfs /dev/SPEED/node02

#create snapshot

lvcreate -L10G -s -n some-backup /dev/SPEED/some
mount /dev/SPEED/some-backup /mnt/some-backup

#remove snapshot

umount /mnt/some-backup
lvremove /dev/SPEED/some-backup