diff --git a/betree/Cargo.toml b/betree/Cargo.toml
index e0b8a029..63507ced 100644
--- a/betree/Cargo.toml
+++ b/betree/Cargo.toml
@@ -59,6 +59,7 @@ lfu_cache = { git = "https://github.com/parcio/lfu-cache", rev = "haura-v5" }
 rand = { version = "0.8", features = ["std_rng"] }
 
 pmdk = { path = "./pmdk", optional = true }
+rustc-hash = "1.1.0"
 
 [dev-dependencies]
 rand_xorshift = "0.3"
diff --git a/betree/src/checksum.rs b/betree/src/checksum.rs
deleted file mode 100644
index ee194c03..00000000
--- a/betree/src/checksum.rs
+++ /dev/null
@@ -1,194 +0,0 @@
-//! This module provides a `Checksum` trait for verifying data integrity.
-
-use crate::size::{Size, StaticSize};
-use serde::{de::DeserializeOwned, Deserialize, Serialize};
-use std::{error::Error, fmt, hash::Hasher, iter::once};
-use twox_hash;
-
-/// A checksum to verify data integrity.
-pub trait Checksum:
-    Serialize + DeserializeOwned + Size + Clone + Send + Sync + fmt::Debug + 'static
-{
-    /// Builds a new `Checksum`.
-    type Builder: Builder<Self>;
-
-    /// Verifies the contents of the given buffer which consists of multiple
-    /// `u8` slices.
-    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
-        &self,
-        data: I,
-    ) -> Result<(), ChecksumError>;
-
-    /// Verifies the contents of the given buffer.
-    fn verify(&self, data: &[u8]) -> Result<(), ChecksumError> {
-        self.verify_buffer(once(data))
-    }
-
-    /// Create a valid empty builder for this checksum type.
-    fn builder() -> Self::Builder;
-}
-
-/// A checksum builder
-pub trait Builder<C: Checksum>:
-    Serialize + DeserializeOwned + Clone + Send + Sync + fmt::Debug + 'static
-{
-    /// The internal state of the checksum.
-    type State: State<Checksum = C>;
-
-    /// Create a new state to build a checksum.
-    fn build(&self) -> Self::State;
-}
-
-/// Holds a state for building a new `Checksum`.
-pub trait State {
-    /// The resulting `Checksum`.
-    type Checksum: Checksum;
-
-    /// Ingests the given data into the state.
-    fn ingest(&mut self, data: &[u8]);
-
-    /// Builds the actual `Checksum`.
-    fn finish(self) -> Self::Checksum;
-}
-
-/// This is the error that will be returned when a `Checksum` does not match.
-#[derive(Debug)]
-pub struct ChecksumError;
-
-impl fmt::Display for ChecksumError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        writeln!(f, "Failed to verify the integrity")
-    }
-}
-
-impl Error for ChecksumError {
-    fn description(&self) -> &str {
-        "a checksum error occurred"
-    }
-}
-
-/// `XxHash` contains a digest of `xxHash`
-/// which is an "extremely fast non-cryptographic hash algorithm"
-/// (<https://github.com/Cyan4973/xxHash>)
-#[derive(Serialize, Deserialize, Clone, Copy, Debug, PartialEq, Eq)]
-pub struct XxHash(u64);
-
-impl StaticSize for XxHash {
-    fn static_size() -> usize {
-        8
-    }
-}
-
-impl Checksum for XxHash {
-    type Builder = XxHashBuilder;
-
-    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
-        &self,
-        data: I,
-    ) -> Result<(), ChecksumError> {
-        let mut state = XxHashBuilder.build();
-        for x in data {
-            state.ingest(x.as_ref());
-        }
-        let other = state.finish();
-        if *self == other {
-            Ok(())
-        } else {
-            Err(ChecksumError)
-        }
-    }
-
-    fn builder() -> Self::Builder {
-        XxHashBuilder
-    }
-}
-
-/// The corresponding `Builder` for `XxHash`.
-#[derive(Clone, Debug, Serialize, Deserialize)]
-pub struct XxHashBuilder;
-
-impl Builder<XxHash> for XxHashBuilder {
-    type State = XxHashState;
-
-    fn build(&self) -> Self::State {
-        XxHashState(twox_hash::XxHash::with_seed(0))
-    }
-}
-
-/// The internal state of `XxHash`.
-pub struct XxHashState(twox_hash::XxHash);
-
-impl State for XxHashState {
-    type Checksum = XxHash;
-
-    fn ingest(&mut self, data: &[u8]) {
-        self.0.write(data);
-    }
-
-    fn finish(self) -> Self::Checksum {
-        XxHash(self.0.finish())
-    }
-}
-
-/// The rustc own hash impl originally from Firefox.
-#[derive(Serialize, Deserialize, Clone, Copy, Debug, PartialEq, Eq)]
-pub struct FxHash(u64);
-
-impl StaticSize for FxHash {
-    fn static_size() -> usize {
-        8
-    }
-}
-
-impl Checksum for FxHash {
-    type Builder = FxHashBuilder;
-
-    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
-        &self,
-        data: I,
-    ) -> Result<(), ChecksumError> {
-        let mut state = FxHashBuilder.build();
-        for x in data {
-            state.ingest(x.as_ref());
-        }
-        let other = state.finish();
-        if *self == other {
-            Ok(())
-        } else {
-            Err(ChecksumError)
-        }
-    }
-
-    fn builder() -> Self::Builder {
-        FxHashBuilder
-    }
-}
-
-/// The corresponding `Builder` for `XxHash`.
-#[derive(Clone, Debug, Serialize, Deserialize)]
-pub struct FxHashBuilder;
-
-impl Builder<FxHash> for FxHashBuilder {
-    type State = FxHashState;
-
-    fn build(&self) -> Self::State {
-        FxHashState(FxHasher::default())
-    }
-}
-
-use rustc_hash::FxHasher;
-
-/// The internal state of `XxHash`.
-pub struct FxHashState(FxHasher);
-
-impl State for FxHashState {
-    type Checksum = FxHash;
-
-    fn ingest(&mut self, data: &[u8]) {
-        self.0.write(data);
-    }
-
-    fn finish(self) -> Self::Checksum {
-        FxHash(self.0.finish())
-    }
-}
diff --git a/betree/src/checksum/fxhash.rs b/betree/src/checksum/fxhash.rs
new file mode 100644
index 00000000..dd56c985
--- /dev/null
+++ b/betree/src/checksum/fxhash.rs
@@ -0,0 +1,67 @@
+/// Impl for Checksum for FxHash.
+use super::{Builder, Checksum, ChecksumError, State};
+use crate::size::StaticSize;
+use rustc_hash::FxHasher;
+use serde::{Deserialize, Serialize};
+use std::hash::Hasher;
+
+/// The rustc own hash impl originally from Firefox.
+#[derive(Serialize, Deserialize, Clone, Copy, Debug, PartialEq, Eq)]
+pub struct FxHash(u64);
+
+impl StaticSize for FxHash {
+    fn static_size() -> usize {
+        8
+    }
+}
+
+impl Checksum for FxHash {
+    type Builder = FxHashBuilder;
+
+    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
+        &self,
+        data: I,
+    ) -> Result<(), ChecksumError> {
+        let mut state = FxHashBuilder.build();
+        for x in data {
+            state.ingest(x.as_ref());
+        }
+        let other = state.finish();
+        if *self == other {
+            Ok(())
+        } else {
+            Err(ChecksumError)
+        }
+    }
+
+    fn builder() -> Self::Builder {
+        FxHashBuilder
+    }
+}
+
+/// The corresponding `Builder` for `FxHash`.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct FxHashBuilder;
+
+impl Builder<FxHash> for FxHashBuilder {
+    type State = FxHashState;
+
+    fn build(&self) -> Self::State {
+        FxHashState(FxHasher::default())
+    }
+}
+
+/// The internal state of `XxHash`.
+pub struct FxHashState(FxHasher);
+
+impl State for FxHashState {
+    type Checksum = FxHash;
+
+    fn ingest(&mut self, data: &[u8]) {
+        self.0.write(data);
+    }
+
+    fn finish(self) -> Self::Checksum {
+        FxHash(self.0.finish())
+    }
+}
diff --git a/betree/src/checksum/mod.rs b/betree/src/checksum/mod.rs
new file mode 100644
index 00000000..c4d5c0c4
--- /dev/null
+++ b/betree/src/checksum/mod.rs
@@ -0,0 +1,73 @@
+//! This module provides a `Checksum` trait for verifying data integrity.
+
+use crate::size::Size;
+use serde::{de::DeserializeOwned, Serialize};
+use std::{error::Error, fmt, iter::once};
+
+mod fxhash;
+mod xxhash;
+
+pub use fxhash::{FxHash, FxHashBuilder};
+pub use xxhash::{XxHash, XxHashBuilder};
+
+/// A checksum to verify data integrity.
+pub trait Checksum:
+    Serialize + DeserializeOwned + Size + Clone + Send + Sync + fmt::Debug + 'static
+{
+    /// Builds a new `Checksum`.
+    type Builder: Builder<Self>;
+
+    /// Verifies the contents of the given buffer which consists of multiple
+    /// `u8` slices.
+    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
+        &self,
+        data: I,
+    ) -> Result<(), ChecksumError>;
+
+    /// Verifies the contents of the given buffer.
+    fn verify(&self, data: &[u8]) -> Result<(), ChecksumError> {
+        self.verify_buffer(once(data))
+    }
+
+    /// Create a valid empty builder for this checksum type.
+    fn builder() -> Self::Builder;
+}
+
+/// A checksum builder
+pub trait Builder<C: Checksum>:
+    Serialize + DeserializeOwned + Clone + Send + Sync + fmt::Debug + 'static
+{
+    /// The internal state of the checksum.
+    type State: State<Checksum = C>;
+
+    /// Create a new state to build a checksum.
+    fn build(&self) -> Self::State;
+}
+
+/// Holds a state for building a new `Checksum`.
+pub trait State {
+    /// The resulting `Checksum`.
+    type Checksum: Checksum;
+
+    /// Ingests the given data into the state.
+    fn ingest(&mut self, data: &[u8]);
+
+    /// Builds the actual `Checksum`.
+    fn finish(self) -> Self::Checksum;
+}
+
+/// This is the error that will be returned when a `Checksum` does not match.
+#[derive(Debug)]
+pub struct ChecksumError;
+
+impl fmt::Display for ChecksumError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        writeln!(f, "Failed to verify the integrity")
+    }
+}
+
+impl Error for ChecksumError {
+    fn description(&self) -> &str {
+        "a checksum error occurred"
+    }
+}
diff --git a/betree/src/checksum/xxhash.rs b/betree/src/checksum/xxhash.rs
new file mode 100644
index 00000000..de0c0afd
--- /dev/null
+++ b/betree/src/checksum/xxhash.rs
@@ -0,0 +1,67 @@
+/// `XxHash` contains a digest of `xxHash`
+/// which is an "extremely fast non-cryptographic hash algorithm"
+/// (<https://github.com/Cyan4973/xxHash>)
+use super::{Builder, Checksum, ChecksumError, State};
+use crate::size::StaticSize;
+use serde::{Deserialize, Serialize};
+use std::hash::Hasher;
+
+#[derive(Serialize, Deserialize, Clone, Copy, Debug, PartialEq, Eq)]
+pub struct XxHash(u64);
+
+impl StaticSize for XxHash {
+    fn static_size() -> usize {
+        8
+    }
+}
+
+impl Checksum for XxHash {
+    type Builder = XxHashBuilder;
+
+    fn verify_buffer<I: IntoIterator<Item = T>, T: AsRef<[u8]>>(
+        &self,
+        data: I,
+    ) -> Result<(), ChecksumError> {
+        let mut state = XxHashBuilder.build();
+        for x in data {
+            state.ingest(x.as_ref());
+        }
+        let other = state.finish();
+        if *self == other {
+            Ok(())
+        } else {
+            Err(ChecksumError)
+        }
+    }
+
+    fn builder() -> Self::Builder {
+        XxHashBuilder
+    }
+}
+
+/// The corresponding `Builder` for `XxHash`.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct XxHashBuilder;
+
+impl Builder<XxHash> for XxHashBuilder {
+    type State = XxHashState;
+
+    fn build(&self) -> Self::State {
+        XxHashState(twox_hash::XxHash::with_seed(0))
+    }
+}
+
+/// The internal state of `XxHash`.
+pub struct XxHashState(twox_hash::XxHash);
+
+impl State for XxHashState {
+    type Checksum = XxHash;
+
+    fn ingest(&mut self, data: &[u8]) {
+        self.0.write(data);
+    }
+
+    fn finish(self) -> Self::Checksum {
+        XxHash(self.0.finish())
+    }
+}