Perform the following steps:
1. Type "fdisk -l" without quotes at server system console. This will list all the partitions (including external drive)
2. You have to do a little bit of guessing works as to which partition say hdb1 or hdc1 or sdb1 or sdc1 can be your external drive partition.
3. Create a folder under /mnt say: mkdir /mnt/external
4. Mount the external drive partition using the following command: mount -t vfat /dev/sdb1 /mnt/external (assuming sdb1 is external drive partition)
5. Copy using the copy command. As you said you want to copy everything in home directory so the command will be: cp -arvp /home/. /mnt/external
I hope this helps.