diff --git a/backup.sh b/backup.sh
index cfc0188..9c05593 100755
--- a/backup.sh
+++ b/backup.sh
@@ -2,6 +2,29 @@
 
 BAKRNG_ROOT=`cat rootzfs.txt`
 
+## Data Format
+
+### user.txt
+# <username>
+
+### hosts.txt
+# <host 1 address> <host 1 port> <host 1 root zfs>
+# <host 2 address> <host 2 port> <host 2 root zfs>
+# ...
+
+### rootzfs.txt
+# <root zfs>
+
+### datasets.txt
+# <dataset 1>
+# <dataset 1>/<dataset 1a>
+# <dataset 1>/<dataset 1b>
+# <dataset 2>
+# <dataset 2>/<dataset 2a>
+# <dataset 3>
+# ...
+
+
 if [ ! -f user.txt ]; then echo "No user specified."; exit 2; fi
 if [ ! -f hosts.txt ]; then echo "No hosts specified."; exit 2; fi
 if [ ! -f rootzfs.txt ]; then echo "No rootzfs specified."; exit 2; fi