diff --git a/src/backup/chunk_store.rs b/src/backup/chunk_store.rs
new file mode 100644
index 00000000..d376a5b4
--- /dev/null
+++ b/src/backup/chunk_store.rs
@@ -0,0 +1,74 @@
+use failure::*;
+use std::path::{Path, PathBuf};
+
+pub struct ChunkStore {
+    base: PathBuf,
+    chunk_dir: PathBuf,
+}
+
+// see RFC4648 for base32hex definition
+const BASE32HEX_ALPHABET: &'static [u8; 32]   = b"0123456789ABCDEFGHIJKLMNOPQRSTUV";
+
+fn u10_to_base32hex(num: usize) -> String {
+    let lo = num & 0b11111 as usize;
+    let hi = num >> 5 as usize;
+    format!("{}{}", BASE32HEX_ALPHABET[hi] as char, BASE32HEX_ALPHABET[lo] as char)
+}
+
+impl ChunkStore {
+
+    fn new<P: Into<PathBuf>>(path: P) -> Self {
+        let base = path.into();
+        let mut chunk_dir = base.clone();
+        chunk_dir.push(".chunks");
+
+        ChunkStore { base, chunk_dir }
+    }
+
+    pub fn create<P: Into<PathBuf>>(path: P) -> Result<Self, Error> {
+
+        let me = Self::new(path);
+
+        std::fs::create_dir(&me.base)?;
+        std::fs::create_dir(&me.chunk_dir)?;
+
+        // create 1024 subdir
+        for i in 0..1024 {
+            let mut l1path = me.base.clone();
+            l1path.push(u10_to_base32hex(i));
+            std::fs::create_dir(&l1path)?;
+        }
+
+        Ok(me)
+    }
+
+    pub fn open<P: Into<PathBuf>>(path: P) -> Result<Self, Error> {
+
+        let me = Self::new(path);
+
+        let metadata = std::fs::metadata(&me.chunk_dir)?;
+
+        println!("{:?}", metadata.file_type());
+
+        Ok(me)
+    }
+
+}
+
+
+#[test]
+fn test_chunk_store1() {
+
+    if let Err(_e) = std::fs::remove_dir_all(".testdir") { /* ignore */ }
+
+    let chunk_store = ChunkStore::open(".testdir");
+    assert!(chunk_store.is_err());
+
+    let chunk_store = ChunkStore::create(".testdir");
+    assert!(chunk_store.is_ok());
+
+    let chunk_store = ChunkStore::create(".testdir");
+    assert!(chunk_store.is_err());
+
+
+}
diff --git a/src/lib.rs b/src/lib.rs
index 2410a8a0..0d800d05 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -30,6 +30,11 @@ pub mod server {
 
 pub mod section_config;
 
+pub mod backup {
+
+    pub mod chunk_store;
+}
+
 pub mod storage {
 
     pub mod config;