diff --git a/src/main.rs b/src/main.rs
index 3c4b4cd..dc7a125 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -213,6 +213,9 @@ fn main() -> Result<()> {
                             println!("Added new storage.");
                             trace!("Finished adding storage");
                         }
+                        StorageType::SubDirectory => {
+                            todo!()
+                        }
                     }
                 }
                 StorageCommands::List {} => {
diff --git a/src/storages.rs b/src/storages.rs
index f1ae006..457924c 100644
--- a/src/storages.rs
+++ b/src/storages.rs
@@ -1,10 +1,11 @@
 //! Manipulates storages.
 
+use crate::storages::directory::Directory;
+use crate::storages::physical_drive_partition::PhysicalDrivePartition;
 use anyhow::{anyhow, Context, Result};
 use clap::ValueEnum;
-use physical_drive_partition::PhysicalDrivePartition;
 use serde::{Deserialize, Serialize};
-use std::{ffi, fmt, fs, path::Path, io};
+use std::{ffi, fmt, fs, io, path::Path};
 
 /// YAML file to store known storages..
 pub const STORAGESFILE: &str = "storages.yml";
@@ -12,6 +13,7 @@ pub const STORAGESFILE: &str = "storages.yml";
 #[derive(ValueEnum, Clone, Copy, Debug)]
 pub enum StorageType {
     Physical,
+    SubDirectory,
     // Online,
 }
 
@@ -19,6 +21,7 @@ pub enum StorageType {
 #[derive(Serialize, Deserialize, Debug)]
 pub enum Storage {
     PhysicalStorage(PhysicalDrivePartition),
+    SubDirectory(Directory),
     // /// Online storage provided by others.
     // OnlineStorage {
     //     name: String,
@@ -28,9 +31,14 @@ pub enum Storage {
 }
 
 impl Storage {
-    pub fn add_alias(&mut self, disk: &sysinfo::Disk, config_dir: &std::path::PathBuf) -> anyhow::Result<()> {
+    pub fn add_alias(
+        &mut self,
+        disk: &sysinfo::Disk,
+        config_dir: &std::path::PathBuf,
+    ) -> anyhow::Result<()> {
         match self {
             Self::PhysicalStorage(s) => s.add_alias(disk, config_dir),
+            Self::SubDirectory(_) => Err(anyhow!("SubDirectory doesn't have system alias.")),
         }
     }
 }
@@ -39,15 +47,16 @@ impl StorageExt for Storage {
     fn name(&self) -> &String {
         match self {
             Self::PhysicalStorage(s) => s.name(),
+            Self::SubDirectory(s) => s.name(),
         }
     }
-
 }
 
 impl fmt::Display for Storage {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::PhysicalStorage(s) => s.fmt(f),
+            Self::SubDirectory(s) => s.fmt(f),
         }
     }
 }
@@ -57,6 +66,7 @@ pub trait StorageExt {
     fn name(&self) -> &String;
 }
 
+pub mod directory;
 pub mod physical_drive_partition;
 
 /// Get `Vec<Storage>` from devices.yml([DEVICESFILE]).
@@ -91,4 +101,4 @@ pub fn write_storages(config_dir: &Path, storages: Vec<Storage>) -> Result<()> {
     let f = fs::File::create(config_dir.join(STORAGESFILE))?;
     let writer = io::BufWriter::new(f);
     serde_yaml::to_writer(writer, &storages).map_err(|e| anyhow!(e))
-}
\ No newline at end of file
+}
diff --git a/src/storages/directory.rs b/src/storages/directory.rs
new file mode 100644
index 0000000..f50cf1c
--- /dev/null
+++ b/src/storages/directory.rs
@@ -0,0 +1,49 @@
+//! Manipulate subdirectories of other storages, including directories.
+
+use serde::{Deserialize, Serialize};
+use std::{path, fmt::{self, write}, rc::Rc};
+
+use super::{Storage, StorageExt};
+
+/// Subdirectory of other [Storage]s.
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Directory {
+    name: String,
+    parent: Box<Storage>,
+    relative_path: path::PathBuf,
+    notes: String,
+}
+
+impl Directory {
+    /// - `name`: id
+    /// - `parent`: where the directory locates.
+    /// - `relative_path`: path from root of the parent storage.
+    /// - `notes`: supplimental notes.
+    pub fn new(
+        name: String,
+        parent: Rc<Storage>, // todo implement serialize
+        relative_path: path::PathBuf,
+        notes: String,
+    ) -> Directory {
+        Directory {name, parent, relative_path, notes}
+    }
+}
+
+impl StorageExt for Directory {
+    fn name(&self) -> &String {
+        &self.name
+    }
+}
+
+impl fmt::Display for Directory {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "S {name:<10} < {parent:<10}{relative_path:<10} : {notes}",
+            name = self.name(),
+            parent = self.parent,
+            relative_path = self.relative_path.display(),
+            notes = self.notes,
+        )
+    }
+}
\ No newline at end of file
diff --git a/src/storages/physical_drive_partition.rs b/src/storages/physical_drive_partition.rs
index 3f3a2b2..0b5d934 100644
--- a/src/storages/physical_drive_partition.rs
+++ b/src/storages/physical_drive_partition.rs
@@ -80,7 +80,7 @@ impl fmt::Display for PhysicalDrivePartition {
         let removable_indicator = if self.is_removable { "+" } else { "-" };
         write!(
             f,
-            "{name:<10} {size}  {removable:<1} {kind:<6} {fs:<5}",
+            "P {name:<10} {size}  {removable:<1} {kind:<6} {fs:<5}",
             name = self.name(),
             size = Byte::from_bytes(self.capacity.into()).get_appropriate_unit(true),
             removable = removable_indicator,