diff --git a/storage/src/block/iterator.rs b/storage/src/block/iterator.rs
index fb9103d..a12693c 100644
--- a/storage/src/block/iterator.rs
+++ b/storage/src/block/iterator.rs
@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use bytes::{Buf, Bytes};
+use bytes::Buf;
 
 use crate::block::Block;
 
@@ -134,7 +134,7 @@ mod test {
             let value = block_iterator.value();
 
             keys_res.push(key[0]);
-            values_res.push(from_utf8(&value).unwrap().to_string());
+            values_res.push(from_utf8(value).unwrap().to_string());
 
             block_iterator.next();
         }
@@ -176,7 +176,7 @@ mod test {
             let value = block_iterator.value();
 
             keys_res.push(key[0]);
-            values_res.push(from_utf8(&value).unwrap().to_string());
+            values_res.push(from_utf8(value).unwrap().to_string());
 
             block_iterator.next();
         }
diff --git a/storage/src/iterators/lsm_iterator.rs b/storage/src/iterators/lsm_iterator.rs
index a1e6de4..72c2cfa 100644
--- a/storage/src/iterators/lsm_iterator.rs
+++ b/storage/src/iterators/lsm_iterator.rs
@@ -1,19 +1,31 @@
-use anyhow::Ok;
+use std::ops::Bound;
+
+use anyhow::{Ok, Result};
+use bytes::Bytes;
 
 use crate::{
-    common::iterator::StorageIterator, iterators::merged_iterator::MergedIterator,
+    SSTableIterator,
+    common::iterator::StorageIterator,
+    iterators::{merged_iterator::MergedIterator, two_merge_iterator::TwoMergeIterator},
     memtable::memtable_iterator::MemtableIterator,
 };
 
-type LsmIteratorInner = MergedIterator<MemtableIterator>;
+type LsmIteratorInner =
+    TwoMergeIterator<MergedIterator<MemtableIterator>, MergedIterator<SSTableIterator>>;
 
 pub struct LsmIterator {
     inner: LsmIteratorInner,
+    end_bound: Bound<Bytes>,
+    valid: bool,
 }
 
 impl LsmIterator {
-    pub fn new(iter: LsmIteratorInner) -> Self {
-        let mut lsm_iterator = Self { inner: iter };
+    pub fn new(iter: LsmIteratorInner, upper: Bound<Bytes>) -> Self {
+        let mut lsm_iterator = Self {
+            inner: iter,
+            end_bound: upper,
+            valid: true,
+        };
         lsm_iterator.skip_deleted();
 
         lsm_iterator
@@ -36,12 +48,24 @@ impl StorageIterator for LsmIterator {
     }
 
     fn is_valid(&self) -> bool {
-        self.inner.is_valid()
+        self.valid
     }
 
-    fn next(&mut self) -> anyhow::Result<()> {
-        let _ = self.inner.next();
+    fn next(&mut self) -> Result<()> {
+        self.inner.next()?;
+
+        if !self.inner.is_valid() {
+            self.valid = false;
+            return Ok(());
+        }
+
         self.skip_deleted();
+
+        match self.end_bound.as_ref() {
+            Bound::Unbounded => {}
+            Bound::Included(key) => self.valid = self.inner.key() <= &key[..],
+            Bound::Excluded(key) => self.valid = self.inner.key() < &key[..],
+        };
         Ok(())
     }
 }
diff --git a/storage/src/iterators/two_merge_iterator.rs b/storage/src/iterators/two_merge_iterator.rs
index e60bdc6..6835b50 100644
--- a/storage/src/iterators/two_merge_iterator.rs
+++ b/storage/src/iterators/two_merge_iterator.rs
@@ -1,4 +1,4 @@
-use std::{cmp::Ordering, str::from_utf8};
+use std::cmp::Ordering;
 
 use anyhow::{Ok, Result};
 
@@ -18,7 +18,7 @@ impl<T: 'static + StorageIterator, W: 'static + StorageIterator> TwoMergeIterato
             match mem_iter.key().cmp(sst_iter.key()) {
                 Ordering::Equal => mem_iter.is_valid(),
                 Ordering::Less => mem_iter.is_valid(),
-                Ordering::Greater => false,
+                Ordering::Greater => !sst_iter.is_valid(), // use mem_iter if sst_iter is invalid
             }
         };
 
@@ -48,7 +48,10 @@ impl<T: 'static + StorageIterator, W: 'static + StorageIterator> StorageIterator
     }
 
     fn is_valid(&self) -> bool {
-        self.mem_iter.is_valid() || self.sst_iter.is_valid()
+        match self.is_mem {
+            true => self.mem_iter.is_valid(),
+            _ => self.sst_iter.is_valid(),
+        }
     }
 
     fn next(&mut self) -> Result<()> {
@@ -67,7 +70,7 @@ impl<T: 'static + StorageIterator, W: 'static + StorageIterator> StorageIterator
             match self.mem_iter.key().cmp(self.sst_iter.key()) {
                 Ordering::Equal => self.mem_iter.is_valid(),
                 Ordering::Less => self.mem_iter.is_valid(),
-                Ordering::Greater => false,
+                Ordering::Greater => !self.sst_iter.is_valid(),
             }
         };
 
diff --git a/storage/src/lsm_storage.rs b/storage/src/lsm_storage.rs
index d99b992..64c1711 100644
--- a/storage/src/lsm_storage.rs
+++ b/storage/src/lsm_storage.rs
@@ -1,19 +1,26 @@
 use std::{
+    collections::HashMap,
     ops::Bound,
     sync::{Arc, Mutex, MutexGuard, RwLock},
 };
 
 use crate::{
-    common::errors::KeyNotFound,
-    iterators::{lsm_iterator::LsmIterator, merged_iterator::MergedIterator},
-    memtable::table::Memtable,
+    SSTable, SSTableIterator,
+    common::{errors::KeyNotFound, iterator::StorageIterator},
+    iterators::{
+        lsm_iterator::LsmIterator, merged_iterator::MergedIterator,
+        two_merge_iterator::TwoMergeIterator,
+    },
+    memtable::{memtable_iterator::map_bound, table::Memtable},
+    sst::BlockCache,
 };
 use anyhow::Result;
 use bytes::Bytes;
 
 #[derive(Debug)]
 pub struct Storage {
-    state: RwLock<StorageState>,
+    state: RwLock<Arc<StorageState>>,
+    block_cache: Arc<BlockCache>,
     state_lock: Mutex<()>,
     config: Config,
 }
@@ -22,6 +29,8 @@ pub struct Storage {
 struct StorageState {
     memtable: Arc<Memtable>,
     frozen_memtables: Vec<Arc<Memtable>>,
+    l0_sstables: Vec<usize>,
+    sstables: HashMap<usize, Arc<SSTable>>,
 }
 
 #[derive(Debug)]
@@ -33,10 +42,13 @@ pub fn new(config: Config) -> Storage {
     Storage {
         config,
         state_lock: Mutex::new(()),
-        state: RwLock::new(StorageState {
+        block_cache: Arc::new(BlockCache::new(1 << 20)), // 4gb cache
+        state: RwLock::new(Arc::new(StorageState {
             memtable: Arc::new(Memtable::default()),
             frozen_memtables: Vec::new(),
-        }),
+            l0_sstables: vec![],
+            sstables: HashMap::new(),
+        })),
     }
 }
 
@@ -70,19 +82,46 @@ impl Storage {
         Ok(value)
     }
 
-    pub fn scan(&self, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> LsmIterator {
-        let guard = self.state.read().unwrap();
+    pub fn scan(&self, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> Result<LsmIterator> {
+        let state = {
+            let guard = self.state.read().unwrap();
+            guard.clone()
+        };
+
         let mut iters = vec![];
 
         // insert memtables from newest to oldest
-        iters.push(guard.memtable.scan(lower, upper));
+        iters.push(state.memtable.scan(lower, upper));
 
-        let frozen_tables = &guard.frozen_memtables;
+        let frozen_tables = &state.frozen_memtables;
         for frozen_table in frozen_tables {
             iters.push(frozen_table.scan(lower, upper));
         }
+        let mem_iters = MergedIterator::new(iters);
+
+        let mut table_iters = Vec::with_capacity(state.l0_sstables.len());
+        // TODO: only consider sstables that might contain the key
+        for table_id in state.l0_sstables.iter() {
+            let table = state.sstables[table_id].clone();
+            let iter = match lower {
+                Bound::Included(key) => SSTableIterator::create_and_seek_to_key(table, key)?,
+                Bound::Unbounded => SSTableIterator::create_and_seek_to_first(table)?,
+                Bound::Excluded(key) => {
+                    let mut iter = SSTableIterator::create_and_seek_to_key(table, key)?;
+
+                    if iter.is_valid() && iter.key() == key {
+                        iter.next()?;
+                    }
+                    iter
+                }
+            };
 
-        LsmIterator::new(MergedIterator::new(iters))
+            table_iters.push(iter);
+        }
+
+        let sst_iters = MergedIterator::new(table_iters);
+        let inner = TwoMergeIterator::create(mem_iters, sst_iters).unwrap();
+        Ok(LsmIterator::new(inner, map_bound(upper)))
     }
 
     fn try_freeze(&self, size: usize) {
@@ -98,8 +137,17 @@ impl Storage {
 
         // check again, another thread might have frozen the memtable already.
         if memtable.get_size() >= self.config.sst_size {
-            guard.frozen_memtables.insert(0, memtable);
-            guard.memtable = Arc::new(Memtable::default());
+            let mut frozen_memtables = guard.frozen_memtables.clone();
+            frozen_memtables.insert(0, memtable);
+
+            *guard = Arc::new(StorageState {
+                memtable: Arc::new(Memtable::default()),
+                frozen_memtables,
+                l0_sstables: guard.l0_sstables.clone(),
+                sstables: guard.sstables.clone(),
+            });
+
+            drop(guard);
         }
     }
 }
diff --git a/storage/src/sst/mod.rs b/storage/src/sst/mod.rs
index ebdb1e3..13b83ee 100644
--- a/storage/src/sst/mod.rs
+++ b/storage/src/sst/mod.rs
@@ -7,4 +7,4 @@ mod table;
 pub use builder::SSTableBuilder;
 pub use file::FileObject;
 pub use iterator::SSTableIterator;
-pub use table::SSTable;
+pub use table::{BlockCache, SSTable};
diff --git a/storage/tests/storage.rs b/storage/tests/storage.rs
index 4cca8ca..dd3cf96 100644
--- a/storage/tests/storage.rs
+++ b/storage/tests/storage.rs
@@ -67,7 +67,7 @@ fn scan_items() {
     let mut expected_keys = vec![];
     let mut expected_values = vec![];
 
-    let mut iter = storage.scan(Unbounded, Unbounded);
+    let mut iter = storage.scan(Unbounded, Unbounded).unwrap();
     while iter.is_valid() {
         expected_keys.push(iter.key().to_vec());
         expected_values.push(iter.value().to_vec());
diff --git a/storage/tests/two_merge_iter.rs b/storage/tests/two_merge_iter.rs
index da590d8..07b9e1f 100644
--- a/storage/tests/two_merge_iter.rs
+++ b/storage/tests/two_merge_iter.rs
@@ -117,17 +117,6 @@ fn create_empty_merged_iter() -> MergedIterator<MemtableIterator> {
     MergedIterator::new(iterators)
 }
 
-fn create_empty_sst_iter() -> SSTableIterator {
-    let mut sst_builder = SSTableBuilder::new(32); // block size of 32 bytes
-    let block_cache = Arc::new(Cache::new(1));
-    let tmp_file = NamedTempFile::new().unwrap();
-    let sst = sst_builder
-        .build(1, block_cache.clone(), tmp_file.path())
-        .unwrap();
-
-    SSTableIterator::create_and_seek_to_first(Arc::new(sst)).unwrap()
-}
-
 fn get_sst_entries() -> Vec<(&'static [u8], &'static [u8])> {
     vec![
         (b"b", b"-2"),