diff --git a/runtime/src/accounts.rs b/runtime/src/accounts.rs
index e3d69f1c5d..a6af53560b 100644
--- a/runtime/src/accounts.rs
+++ b/runtime/src/accounts.rs
@@ -1,6 +1,6 @@
 use crate::accounts_db::{
-    get_paths_vec, AccountInfo, AccountStorageSlice, AccountsDB, ErrorCounters,
-    InstructionAccounts, InstructionLoaders,
+    get_paths_vec, AccountInfo, AccountStorage, AccountsDB, ErrorCounters, InstructionAccounts,
+    InstructionLoaders,
 };
 use crate::accounts_index::{AccountsIndex, Fork};
 use crate::append_vec::StoredAccount;
@@ -140,7 +140,7 @@ impl Accounts {
     }
 
     fn load_tx_accounts(
-        storage: &AccountStorageSlice,
+        storage: &AccountStorage,
         ancestors: &HashMap<Fork, usize>,
         accounts_index: &AccountsIndex<AccountInfo>,
         tx: &Transaction,
@@ -180,7 +180,7 @@ impl Accounts {
     }
 
     fn load_executable_accounts(
-        storage: &AccountStorageSlice,
+        storage: &AccountStorage,
         ancestors: &HashMap<Fork, usize>,
         accounts_index: &AccountsIndex<AccountInfo>,
         program_id: &Pubkey,
@@ -222,7 +222,7 @@ impl Accounts {
 
     /// For each program_id in the transaction, load its loaders.
     fn load_loaders(
-        storage: &AccountStorageSlice,
+        storage: &AccountStorage,
         ancestors: &HashMap<Fork, usize>,
         accounts_index: &AccountsIndex<AccountInfo>,
         tx: &Transaction,
diff --git a/runtime/src/accounts_db.rs b/runtime/src/accounts_db.rs
index 5f4955d7c5..a3f120310b 100644
--- a/runtime/src/accounts_db.rs
+++ b/runtime/src/accounts_db.rs
@@ -63,8 +63,7 @@ pub struct AccountInfo {
 }
 /// An offset into the AccountsDB::storage vector
 type AppendVecId = usize;
-type AccountStorage = Vec<Arc<AccountStorageEntry>>;
-pub type AccountStorageSlice = [Arc<AccountStorageEntry>];
+pub type AccountStorage = HashMap<usize, Arc<AccountStorageEntry>>;
 pub type InstructionAccounts = Vec<Account>;
 pub type InstructionLoaders = Vec<Vec<(Pubkey, Account)>>;
 
@@ -87,6 +86,8 @@ impl From<usize> for AccountStorageStatus {
 
 /// Persistent storage structure holding the accounts
 pub struct AccountStorageEntry {
+    id: AppendVecId,
+
     fork_id: Fork,
 
     /// storage holding the accounts
@@ -110,6 +111,7 @@ impl AccountStorageEntry {
         let accounts = AppendVec::new(&path.join(ACCOUNT_DATA_FILE), true, file_size as usize);
 
         AccountStorageEntry {
+            id,
             fork_id,
             accounts,
             count: AtomicUsize::new(0),
@@ -129,13 +131,10 @@ impl AccountStorageEntry {
         self.count.fetch_add(1, Ordering::Relaxed);
     }
 
-    fn remove_account(&self) -> bool {
+    fn remove_account(&self) {
         if self.count.fetch_sub(1, Ordering::Relaxed) == 1 {
             self.accounts.reset();
             self.set_status(AccountStorageStatus::StorageAvailable);
-            true
-        } else {
-            false
         }
     }
 }
@@ -171,7 +170,7 @@ impl AccountsDB {
         let paths = get_paths_vec(&paths);
         AccountsDB {
             accounts_index: RwLock::new(AccountsIndex::default()),
-            storage: RwLock::new(vec![]),
+            storage: RwLock::new(HashMap::new()),
             next_id: AtomicUsize::new(0),
             write_version: AtomicUsize::new(0),
             paths,
@@ -193,7 +192,7 @@ impl AccountsDB {
     }
 
     pub fn has_accounts(&self, fork: Fork) -> bool {
-        for x in self.storage.read().unwrap().iter() {
+        for x in self.storage.read().unwrap().values() {
             if x.fork_id == fork && x.count.load(Ordering::Relaxed) > 0 {
                 return true;
             }
@@ -213,7 +212,7 @@ impl AccountsDB {
             .storage
             .read()
             .unwrap()
-            .iter()
+            .values()
             .filter(|store| store.fork_id == fork_id)
             .cloned()
             .collect();
@@ -231,7 +230,7 @@ impl AccountsDB {
     }
 
     pub fn load(
-        storage: &AccountStorageSlice,
+        storage: &AccountStorage,
         ancestors: &HashMap<Fork, usize>,
         accounts_index: &AccountsIndex<AccountInfo>,
         pubkey: &Pubkey,
@@ -239,7 +238,7 @@ impl AccountsDB {
         let info = accounts_index.get(pubkey, ancestors)?;
         //TODO: thread this as a ref
         storage
-            .get(info.id)
+            .get(&info.id)
             .and_then(|store| Some(store.accounts.get_account(info.offset)?.0.clone_account()))
     }
 
@@ -249,82 +248,51 @@ impl AccountsDB {
         Self::load(&storage, ancestors, &accounts_index, pubkey)
     }
 
-    fn get_storage_id(&self, fork_id: Fork, start: usize, current: usize) -> usize {
-        let mut id = current;
-        let len: usize;
-        {
-            let stores = self.storage.read().unwrap();
-            len = stores.len();
-            if len > 0 {
-                if id == std::usize::MAX {
-                    id = start % len;
-                    if stores[id].get_status() == AccountStorageStatus::StorageAvailable {
-                        return id;
-                    }
+    fn get_exclusive_storage(&self, fork_id: Fork) -> Arc<AccountStorageEntry> {
+        let mut stores = self.storage.write().unwrap();
+        let mut candidates: Vec<Arc<AccountStorageEntry>> = stores
+            .values()
+            .filter_map(|x| {
+                if x.get_status() == AccountStorageStatus::StorageAvailable && x.fork_id == fork_id
+                {
+                    Some(x.clone())
                 } else {
-                    stores[id].set_status(AccountStorageStatus::StorageFull);
+                    None
                 }
+            })
+            .collect();
+        if candidates.is_empty() {
+            let path_idx = thread_rng().gen_range(0, self.paths.len());
+            let storage = self.new_storage_entry(fork_id, &self.paths[path_idx]);
+            candidates.push(Arc::new(storage));
+        }
 
-                loop {
-                    id = (id + 1) % len;
-                    if fork_id == stores[id].fork_id
-                        && stores[id].get_status() == AccountStorageStatus::StorageAvailable
-                    {
-                        break;
-                    }
-                    if id == start % len {
-                        break;
-                    }
-                }
-            }
-        }
-        if len == 0 || id == start % len {
-            let mut stores = self.storage.write().unwrap();
-            // check if new store was already created
-            if stores.len() == len {
-                let path_idx = thread_rng().gen_range(0, self.paths.len());
-                let storage = self.new_storage_entry(fork_id, &self.paths[path_idx]);
-                stores.push(Arc::new(storage));
-            }
-            id = stores.len() - 1;
-        }
-        id
+        let rv = thread_rng().gen_range(0, candidates.len());
+        stores.remove(&candidates[rv].id);
+        candidates[rv].clone()
     }
 
-    fn append_account(&self, fork_id: Fork, pubkey: &Pubkey, account: &Account) -> (usize, usize) {
-        let offset: usize;
-        let start = self.next_id.fetch_add(1, Ordering::Relaxed);
-        let mut id = self.get_storage_id(fork_id, start, std::usize::MAX);
-
-        // Even if no lamports, need to preserve the account owner so
-        // we can update the vote_accounts correctly if this account is purged
-        // when squashing.
-        let acc = &mut account.clone();
+    fn append_account(
+        &self,
+        storage: &Arc<AccountStorageEntry>,
+        pubkey: &Pubkey,
+        account: &Account,
+    ) -> Option<usize> {
+        let write_version = self.write_version.fetch_add(1, Ordering::Relaxed) as u64;
+        let meta = StorageMeta {
+            write_version,
+            pubkey: *pubkey,
+            data_len: account.data.len() as u64,
+        };
         if account.lamports == 0 {
-            acc.data.resize(0, 0);
+            // Even if no lamports, need to preserve the account owner so
+            // we can update the vote_accounts correctly as roots move forward
+            let account = &mut account.clone();
+            account.data.resize(0, 0);
+            storage.accounts.append_account(meta, account)
+        } else {
+            storage.accounts.append_account(meta, account)
         }
-
-        loop {
-            let result: Option<usize>;
-            {
-                let accounts = &self.storage.read().unwrap()[id];
-                let write_version = self.write_version.fetch_add(1, Ordering::Relaxed) as u64;
-                let meta = StorageMeta {
-                    write_version,
-                    pubkey: *pubkey,
-                    data_len: account.data.len() as u64,
-                };
-                result = accounts.accounts.append_account(meta, account);
-                accounts.add_account();
-            }
-            if let Some(val) = result {
-                offset = val;
-                break;
-            } else {
-                id = self.get_storage_id(fork_id, start, id);
-            }
-        }
-        (id, offset)
     }
 
     pub fn purge_fork(&self, fork: Fork) {
@@ -332,55 +300,107 @@ impl AccountsDB {
         let is_root = self.accounts_index.read().unwrap().is_root(fork);
         trace!("PURGING {} {}", fork, is_root);
         if !is_root {
-            self.storage.write().unwrap().retain(|x| {
-                trace!("PURGING {} {}", x.fork_id, fork);
-                x.fork_id != fork
+            self.storage.write().unwrap().retain(|_, v| {
+                trace!("PURGING {} {}", v.fork_id, fork);
+                v.fork_id != fork
             });
         }
     }
 
+    fn store_accounts(&self, fork_id: Fork, accounts: &[(&Pubkey, &Account)]) -> Vec<AccountInfo> {
+        let mut storage = self.get_exclusive_storage(fork_id);
+        let mut infos = vec![];
+        for (pubkey, account) in accounts {
+            loop {
+                let rv = self.append_account(&storage, pubkey, account);
+                if let Some(offset) = rv {
+                    storage.add_account();
+                    infos.push(AccountInfo {
+                        id: storage.id,
+                        offset,
+                        lamports: account.lamports,
+                    });
+                    break;
+                } else {
+                    storage.set_status(AccountStorageStatus::StorageFull);
+                    self.storage.write().unwrap().insert(storage.id, storage);
+                    storage = self.get_exclusive_storage(fork_id);
+                }
+            }
+        }
+        self.storage.write().unwrap().insert(storage.id, storage);
+        infos
+    }
+
+    fn update_index(
+        &self,
+        fork_id: Fork,
+        infos: Vec<AccountInfo>,
+        accounts: &[(&Pubkey, &Account)],
+    ) -> Vec<(Fork, AccountInfo)> {
+        let mut index = self.accounts_index.write().unwrap();
+        let mut reclaims = vec![];
+        for (i, info) in infos.into_iter().enumerate() {
+            let key = &accounts[i].0;
+            reclaims.extend(index.insert(fork_id, key, info).into_iter())
+        }
+        reclaims
+    }
+
+    fn remove_dead_accounts(&self, reclaims: Vec<(Fork, AccountInfo)>) -> HashSet<Fork> {
+        let storage = self.storage.read().unwrap();
+        for (fork_id, account_info) in reclaims {
+            if let Some(store) = storage.get(&account_info.id) {
+                assert_eq!(
+                    fork_id, store.fork_id,
+                    "AccountDB::accounts_index corrupted. Storage should only point to one fork"
+                );
+                store.remove_account();
+            }
+        }
+        //TODO: performance here could be improved if AccountsDB::storage was organized by fork
+        let dead_forks: HashSet<Fork> = storage
+            .values()
+            .filter_map(|x| {
+                if x.count.load(Ordering::Relaxed) == 0 {
+                    Some(x.fork_id)
+                } else {
+                    None
+                }
+            })
+            .collect();
+        let live_forks: HashSet<Fork> = storage
+            .values()
+            .filter_map(|x| {
+                if x.count.load(Ordering::Relaxed) > 0 {
+                    Some(x.fork_id)
+                } else {
+                    None
+                }
+            })
+            .collect();
+        dead_forks.difference(&live_forks).cloned().collect()
+    }
+    fn cleanup_dead_forks(&self, dead_forks: &mut HashSet<Fork>) {
+        let mut index = self.accounts_index.write().unwrap();
+        // a fork is not totally dead until it is older than the root
+        dead_forks.retain(|fork| *fork < index.last_root);
+        for fork in dead_forks.iter() {
+            index.cleanup_dead_fork(*fork);
+        }
+    }
+
     /// Store the account update.
     pub fn store(&self, fork_id: Fork, accounts: &[(&Pubkey, &Account)]) {
-        //TODO; these blocks should be separate functions and unit tested
-        let infos: Vec<_> = accounts
-            .iter()
-            .map(|(pubkey, account)| {
-                let (id, offset) = self.append_account(fork_id, pubkey, account);
-                AccountInfo {
-                    id,
-                    offset,
-                    lamports: account.lamports,
-                }
-            })
-            .collect();
-
-        let reclaims: Vec<(Fork, AccountInfo)> = {
-            let mut index = self.accounts_index.write().unwrap();
-            let mut reclaims = vec![];
-            for (i, info) in infos.into_iter().enumerate() {
-                let key = &accounts[i].0;
-                reclaims.extend(index.insert(fork_id, key, info).into_iter())
-            }
-            reclaims
-        };
-
-        let dead_forks: HashSet<Fork> = {
-            let stores = self.storage.read().unwrap();
-            let mut cleared_forks: HashSet<Fork> = HashSet::new();
-            for (fork_id, account_info) in reclaims {
-                let cleared = stores[account_info.id].remove_account();
-                if cleared {
-                    cleared_forks.insert(fork_id);
-                }
-            }
-            let live_forks: HashSet<Fork> = stores.iter().map(|x| x.fork_id).collect();
-            cleared_forks.difference(&live_forks).cloned().collect()
-        };
-        {
-            let mut index = self.accounts_index.write().unwrap();
-            for fork in dead_forks {
-                index.cleanup_dead_fork(fork);
-            }
+        let infos = self.store_accounts(fork_id, accounts);
+        let reclaims = self.update_index(fork_id, infos, accounts);
+        trace!("reclaim: {}", reclaims.len());
+        let mut dead_forks = self.remove_dead_accounts(reclaims);
+        trace!("dead_forks: {}", dead_forks.len());
+        self.cleanup_dead_forks(&mut dead_forks);
+        trace!("purge_forks: {}", dead_forks.len());
+        for fork in dead_forks {
+            self.purge_fork(fork);
         }
     }
 
@@ -569,7 +589,6 @@ mod tests {
     }
 
     #[test]
-    #[ignore]
     fn test_accountsdb_count_stores() {
         let paths = get_tmp_accounts_path!();
         let db = AccountsDB::new(&paths.paths);
@@ -592,15 +611,15 @@ mod tests {
         {
             let stores = db.storage.read().unwrap();
             assert_eq!(stores.len(), 2);
-            assert_eq!(stores[0].count.load(Ordering::Relaxed), 2);
-            assert_eq!(stores[1].count.load(Ordering::Relaxed), 2);
+            assert_eq!(stores[&0].count.load(Ordering::Relaxed), 2);
+            assert_eq!(stores[&1].count.load(Ordering::Relaxed), 2);
         }
         db.add_root(1);
         {
             let stores = db.storage.read().unwrap();
             assert_eq!(stores.len(), 2);
-            assert_eq!(stores[0].count.load(Ordering::Relaxed), 2);
-            assert_eq!(stores[1].count.load(Ordering::Relaxed), 2);
+            assert_eq!(stores[&0].count.load(Ordering::Relaxed), 2);
+            assert_eq!(stores[&1].count.load(Ordering::Relaxed), 2);
         }
     }
 
@@ -675,10 +694,10 @@ mod tests {
         let stores = accounts.storage.read().unwrap();
         assert_eq!(stores.len(), 1);
         assert_eq!(
-            stores[0].get_status(),
+            stores[&0].get_status(),
             AccountStorageStatus::StorageAvailable
         );
-        stores[0].count.load(Ordering::Relaxed) == count
+        stores[&0].count.load(Ordering::Relaxed) == count
     }
 
     fn check_accounts(accounts: &AccountsDB, pubkeys: &Vec<Pubkey>, fork: Fork) {
@@ -745,7 +764,7 @@ mod tests {
         }
 
         let mut append_vec_histogram = HashMap::new();
-        for storage in accounts.storage.read().unwrap().iter() {
+        for storage in accounts.storage.read().unwrap().values() {
             *append_vec_histogram.entry(storage.fork_id).or_insert(0) += 1;
         }
         for count in append_vec_histogram.values() {
@@ -754,7 +773,6 @@ mod tests {
     }
 
     #[test]
-    #[ignore]
     fn test_account_grow() {
         let paths = get_tmp_accounts_path!();
         let accounts = AccountsDB::new(&paths.paths);
@@ -769,8 +787,8 @@ mod tests {
         {
             let stores = accounts.storage.read().unwrap();
             assert_eq!(stores.len(), 1);
-            assert_eq!(stores[0].count.load(Ordering::Relaxed), 1);
-            assert_eq!(stores[0].get_status(), status[0]);
+            assert_eq!(stores[&0].count.load(Ordering::Relaxed), 1);
+            assert_eq!(stores[&0].get_status(), status[0]);
         }
 
         let pubkey2 = Pubkey::new_rand();
@@ -779,10 +797,10 @@ mod tests {
         {
             let stores = accounts.storage.read().unwrap();
             assert_eq!(stores.len(), 2);
-            assert_eq!(stores[0].count.load(Ordering::Relaxed), 1);
-            assert_eq!(stores[0].get_status(), status[1]);
-            assert_eq!(stores[1].count.load(Ordering::Relaxed), 1);
-            assert_eq!(stores[1].get_status(), status[0]);
+            assert_eq!(stores[&0].count.load(Ordering::Relaxed), 1);
+            assert_eq!(stores[&0].get_status(), status[1]);
+            assert_eq!(stores[&1].count.load(Ordering::Relaxed), 1);
+            assert_eq!(stores[&1].get_status(), status[0]);
         }
         let ancestors = vec![(0, 0)].into_iter().collect();
         assert_eq!(accounts.load_slow(&ancestors, &pubkey1).unwrap(), account1);
@@ -794,12 +812,12 @@ mod tests {
             {
                 let stores = accounts.storage.read().unwrap();
                 assert_eq!(stores.len(), 3);
-                assert_eq!(stores[0].count.load(Ordering::Relaxed), count[index]);
-                assert_eq!(stores[0].get_status(), status[0]);
-                assert_eq!(stores[1].count.load(Ordering::Relaxed), 1);
-                assert_eq!(stores[1].get_status(), status[1]);
-                assert_eq!(stores[2].count.load(Ordering::Relaxed), count[index ^ 1]);
-                assert_eq!(stores[2].get_status(), status[0]);
+                assert_eq!(stores[&0].count.load(Ordering::Relaxed), count[index]);
+                assert_eq!(stores[&0].get_status(), status[0]);
+                assert_eq!(stores[&1].count.load(Ordering::Relaxed), 1);
+                assert_eq!(stores[&1].get_status(), status[1]);
+                assert_eq!(stores[&2].count.load(Ordering::Relaxed), count[index ^ 1]);
+                assert_eq!(stores[&2].get_status(), status[0]);
             }
             let ancestors = vec![(0, 0)].into_iter().collect();
             assert_eq!(accounts.load_slow(&ancestors, &pubkey1).unwrap(), account1);
@@ -831,4 +849,41 @@ mod tests {
         assert!(accounts.load_slow(&ancestors, &pubkeys[0]).is_some());
     }
 
+    #[test]
+    fn test_lazy_gc_fork() {
+        //This test is pedantic
+        //A fork is purged when a non root bank is cleaned up.  If a fork is behind root but it is
+        //not root, it means we are retaining dead banks.
+        let paths = get_tmp_accounts_path!();
+        let accounts = AccountsDB::new(&paths.paths);
+        let pubkey = Pubkey::new_rand();
+        let account = Account::new(1, 0, &Account::default().owner);
+        //store an account
+        accounts.store(0, &[(&pubkey, &account)]);
+        let ancestors = vec![(0, 0)].into_iter().collect();
+        let info = accounts
+            .accounts_index
+            .read()
+            .unwrap()
+            .get(&pubkey, &ancestors)
+            .unwrap()
+            .clone();
+        //fork 0 is behind root, but it is not root, therefore it is purged
+        accounts.add_root(1);
+        assert!(accounts.accounts_index.read().unwrap().is_purged(0));
+
+        //fork is still there, since gc is lazy
+        assert!(accounts.storage.read().unwrap().get(&info.id).is_some());
+
+        //store causes cleanup
+        accounts.store(1, &[(&pubkey, &account)]);
+
+        //fork is gone
+        assert!(accounts.storage.read().unwrap().get(&info.id).is_none());
+
+        //new value is there
+        let ancestors = vec![(1, 1)].into_iter().collect();
+        assert_eq!(accounts.load_slow(&ancestors, &pubkey), Some(account));;
+    }
+
 }
diff --git a/runtime/src/accounts_index.rs b/runtime/src/accounts_index.rs
index 0ae3e16e7f..fae7fc1055 100644
--- a/runtime/src/accounts_index.rs
+++ b/runtime/src/accounts_index.rs
@@ -9,7 +9,7 @@ pub struct AccountsIndex<T> {
     account_maps: HashMap<Pubkey, Vec<(Fork, T)>>,
     roots: HashSet<Fork>,
     //This value that needs to be stored to recover the index from AppendVec
-    last_root: Fork,
+    pub last_root: Fork,
 }
 
 impl<T: Clone> AccountsIndex<T> {
@@ -59,7 +59,7 @@ impl<T: Clone> AccountsIndex<T> {
         };
         rv
     }
-    fn is_purged(&self, fork: Fork) -> bool {
+    pub fn is_purged(&self, fork: Fork) -> bool {
         !self.is_root(fork) && fork < self.last_root
     }
     pub fn is_root(&self, fork: Fork) -> bool {