issue about add disk on DN

[ch huang]

hi,all:
        i have a DN,and i mount the two disk ,one disk for
/data/dataspace/1, and one disk for /data/dataspace/2,
the two disk is almost full, so i add a new disk,and modify the config
file,now
disk3 mount on /data/dataspace/3 , is it possible even distribution of data
on the three disks?