Hi, Maybe this is interesting to those who just want to clone used blocks data. The opensource project "Clonezilla" uses udpcast, partimage and DRBL. It will let you multicast clone used blocks data to client machines. For our case, we have 41 clients, the sample M$ Windows XP image size 4.5GB. The average multicast cloning speed could be 0.8 GBytes/min to 1.3 GBytes/min. This make us finish cloning 41 clients in around 10 minutes. The websites are: http://clonezilla.sf.net http://drbl.sf.net http://drbl.nchc.org.tw ps. The Clonezilla server: Intel(R) Pentium(R) 4 CPU 2.80GHz, 1 GB RAM, 2 2-port Intel e1000 NIC. Client: Intel(R) Pentium(R) 4 CPU 2.80GHz, 512 MB RAM, 1 on-board Intel e100 NIC Switch: 2 DLink DES-1026G -24-Port 10/100-T + 2-Port 10/100/1000-T modules. -- Steven Shiau