diff --git a/src/bin/thin_shrink.rs b/src/bin/thin_shrink.rs
index ffb29ad..26b70a4 100644
--- a/src/bin/thin_shrink.rs
+++ b/src/bin/thin_shrink.rs
@@ -25,7 +25,14 @@ fn main() {
                 .value_name("OUTPUT")
                 .takes_value(true),
         )
-        // FIXME: support various disk units
+        .arg(
+            Arg::with_name("DATA")
+                .help("Specify pool data device where data will be moved")
+                .required(true)
+                .long("data")
+                .value_name("DATA")
+                .takes_value(true),
+        )
         .arg(
             Arg::with_name("SIZE")
                 .help("Specify new size for the pool (in data blocks)")
@@ -41,13 +48,14 @@ fn main() {
     let input_file = matches.value_of("INPUT").unwrap();
     let output_file = matches.value_of("OUTPUT").unwrap();
     let size = matches.value_of("SIZE").unwrap().parse::<u64>().unwrap();
+    let data_file = matches.value_of("DATA").unwrap();
 
     if !file_utils::file_exists(input_file) {
         eprintln!("Couldn't find input file '{}'.", &input_file);
         exit(1);
     }
 
-    if let Err(reason) = thinp::shrink::toplevel::shrink(&input_file, &output_file, size) {
+    if let Err(reason) = thinp::shrink::toplevel::shrink(&input_file, &output_file, &data_file, size) {
         println!("Application error: {}\n", reason);
         exit(1);
     }
diff --git a/src/shrink/copier.rs b/src/shrink/copier.rs
new file mode 100644
index 0000000..3df0042
--- /dev/null
+++ b/src/shrink/copier.rs
@@ -0,0 +1,14 @@
+use anyhow::Result;
+
+pub type Sector = u64;
+
+pub struct Region {
+    src: Sector,
+    dest: Sector,
+    len: Sector,
+}
+
+// FIXME: pass in
+pub fn copy(path: &str, regions: &Vec<Region>) -> Result<()> {
+    Ok(())
+}
diff --git a/src/shrink/mod.rs b/src/shrink/mod.rs
index a2c8345..56f9dd5 100644
--- a/src/shrink/mod.rs
+++ b/src/shrink/mod.rs
@@ -1,3 +1,4 @@
 pub mod toplevel;
 
+mod copier;
 mod xml;
diff --git a/src/shrink/toplevel.rs b/src/shrink/toplevel.rs
index 394f9d3..a0f4007 100644
--- a/src/shrink/toplevel.rs
+++ b/src/shrink/toplevel.rs
@@ -5,6 +5,7 @@ use std::io::Write;
 use std::os::unix::fs::OpenOptionsExt;
 
 use crate::shrink::xml;
+use crate::shrink::copier::{self, Region};
 
 //---------------------------------------
 
@@ -268,7 +269,7 @@ fn overlaps(r1: &BlockRange, r2: &BlockRange, index: usize) -> Option<usize> {
 // Finds the index of the first entry that overlaps r.
 fn find_first(r: &BlockRange, remaps: &Vec<(BlockRange, BlockRange)>) -> Option<usize> {
     if remaps.len() == 0 {
-        return None
+        return None;
     }
 
     match remaps.binary_search_by_key(&r.start, |(from, _)| from.start) {
@@ -319,9 +320,9 @@ fn remap(r: &BlockRange, remaps: &Vec<(BlockRange, BlockRange)>) -> Vec<BlockRan
                 }
             }
 
-	    let to = (to.start + (r.start - from.start))..to.end;
-	    let from = r.start..from.end;
-	    println!("to = {:?}", to);
+            let to = (to.start + (r.start - from.start))..to.end;
+            let from = r.start..from.end;
+            println!("to = {:?}", to);
             let rlen = range_len(&r);
             let flen = range_len(&from);
 
@@ -417,6 +418,11 @@ mod tests {
     }
 }
 
+fn build_copy_regions(remaps: &Vec<(BlockRange, BlockRange)>) -> Vec<Region> {
+    let rs = Vec::new();
+    rs
+}
+
 fn process_xml<MV: xml::MetadataVisitor>(input_path: &str, pass: &mut MV) -> Result<()> {
     let input = OpenOptions::new()
         .read(true)
@@ -428,7 +434,7 @@ fn process_xml<MV: xml::MetadataVisitor>(input_path: &str, pass: &mut MV) -> Res
     Ok(())
 }
 
-pub fn shrink(input_path: &str, output_path: &str, nr_blocks: u64) -> Result<()> {
+pub fn shrink(input_path: &str, output_path: &str, data_path: &str, nr_blocks: u64) -> Result<()> {
     let mut pass1 = Pass1::new(nr_blocks);
     process_xml(input_path, &mut pass1);
     eprintln!("{} blocks need moving", pass1.nr_high_blocks);
@@ -465,6 +471,11 @@ pub fn shrink(input_path: &str, output_path: &str, nr_blocks: u64) -> Result<()>
     let remaps = build_remaps(above, free);
     eprintln!("remappings {:?}.", remaps);
 
+    let regions = build_copy_regions(&remaps);
+    eprint!("Copying data...");
+    copier::copy(data_path, &regions);
+    eprintln!("done.");
+
     let output = OpenOptions::new()
         .read(false)
         .write(true)