diff --git a/tests/buffer/file_test.py b/tests/buffer/file_test.py
index 2fcf1242ce..363a4939ad 100644
--- a/tests/buffer/file_test.py
+++ b/tests/buffer/file_test.py
@@ -1,16 +1,23 @@
+import os
 import unittest
 
-from tests.tools import get_template_config, get_unittest_dataset_config
-from trinity.buffer.buffer import get_buffer_reader
+import ray
 
+from tests.tools import (
+    get_checkpoint_path,
+    get_template_config,
+    get_unittest_dataset_config,
+)
+from trinity.buffer.buffer import get_buffer_reader, get_buffer_writer
+from trinity.buffer.utils import default_storage_path
+from trinity.common.config import StorageConfig
+from trinity.common.constants import StorageType
 
-class TestFileReader(unittest.TestCase):
+
+class TestFileBuffer(unittest.TestCase):
     def test_file_reader(self):
         """Test file reader."""
-        config = get_template_config()
-        dataset_config = get_unittest_dataset_config("countdown", "train")
-        config.buffer.explorer_input.taskset = dataset_config
-        reader = get_buffer_reader(config.buffer.explorer_input.taskset, config.buffer)
+        reader = get_buffer_reader(self.config.buffer.explorer_input.taskset, self.config.buffer)
 
         tasks = []
         while True:
@@ -20,9 +27,10 @@ def test_file_reader(self):
                 break
         self.assertEqual(len(tasks), 16)
 
-        config.buffer.explorer_input.taskset.total_epochs = 2
-        config.buffer.explorer_input.taskset.index = 4
-        reader = get_buffer_reader(config.buffer.explorer_input.taskset, config.buffer)
+        # test epoch and offset
+        self.config.buffer.explorer_input.taskset.total_epochs = 2
+        self.config.buffer.explorer_input.taskset.index = 4
+        reader = get_buffer_reader(self.config.buffer.explorer_input.taskset, self.config.buffer)
         tasks = []
         while True:
             try:
@@ -30,3 +38,57 @@ def test_file_reader(self):
             except StopIteration:
                 break
         self.assertEqual(len(tasks), 16 * 2 - 4)
+
+        # test offset > dataset_len
+        self.config.buffer.explorer_input.taskset.total_epochs = 3
+        self.config.buffer.explorer_input.taskset.index = 20
+        reader = get_buffer_reader(self.config.buffer.explorer_input.taskset, self.config.buffer)
+        tasks = []
+        while True:
+            try:
+                tasks.extend(reader.read())
+            except StopIteration:
+                break
+        self.assertEqual(len(tasks), 16 * 3 - 20)
+
+    def test_file_writer(self):
+        writer = get_buffer_writer(
+            self.config.buffer.trainer_input.experience_buffer, self.config.buffer
+        )
+        writer.write(
+            [
+                {"prompt": "hello world"},
+                {"prompt": "hi"},
+            ]
+        )
+        file_wrapper = ray.get_actor("json-test_buffer")
+        self.assertIsNotNone(file_wrapper)
+        file_path = default_storage_path(
+            self.config.buffer.trainer_input.experience_buffer, self.config.buffer
+        )
+        with open(file_path, "r") as f:
+            self.assertEqual(len(f.readlines()), 2)
+
+    def setUp(self):
+        self.config = get_template_config()
+        self.config.checkpoint_root_dir = get_checkpoint_path()
+        dataset_config = get_unittest_dataset_config("countdown", "train")
+        self.config.buffer.explorer_input.taskset = dataset_config
+        self.config.buffer.trainer_input.experience_buffer = StorageConfig(
+            name="test_buffer", storage_type=StorageType.FILE
+        )
+        self.config.buffer.trainer_input.experience_buffer.name = "test_buffer"
+        self.config.buffer.cache_dir = os.path.join(
+            self.config.checkpoint_root_dir, self.config.project, self.config.name, "buffer"
+        )
+        os.makedirs(self.config.buffer.cache_dir, exist_ok=True)
+        if os.path.exists(
+            default_storage_path(
+                self.config.buffer.trainer_input.experience_buffer, self.config.buffer
+            )
+        ):
+            os.remove(
+                default_storage_path(
+                    self.config.buffer.trainer_input.experience_buffer, self.config.buffer
+                )
+            )
diff --git a/tests/buffer/queue_test.py b/tests/buffer/queue_test.py
index 262a2bcd3e..4f3947c795 100644
--- a/tests/buffer/queue_test.py
+++ b/tests/buffer/queue_test.py
@@ -9,7 +9,7 @@
 from trinity.common.constants import AlgorithmType, StorageType
 from trinity.common.experience import Experience
 
-file_path = os.path.join(os.path.dirname(__file__), "test_queue_buffer.jsonl")
+BUFFER_FILE_PATH = os.path.join(os.path.dirname(__file__), "test_queue_buffer.jsonl")
 
 
 class TestQueueBuffer(RayUnittestBase):
@@ -21,7 +21,7 @@ def test_queue_buffer(self):
             name="test_buffer",
             algorithm_type=AlgorithmType.PPO,
             storage_type=StorageType.QUEUE,
-            path=file_path,
+            path=BUFFER_FILE_PATH,
         )
         config = BufferConfig(
             max_retry_times=3,
@@ -61,9 +61,9 @@ def test_queue_buffer(self):
         self.assertEqual(len(exps), put_batch_size * 2)
         writer.finish()
         self.assertRaises(StopIteration, reader.read)
-        with open(file_path, "r") as f:
+        with open(BUFFER_FILE_PATH, "r") as f:
             self.assertEqual(len(f.readlines()), total_num + put_batch_size * 2)
 
     def setUp(self):
-        if os.path.exists(file_path):
-            os.remove(file_path)
+        if os.path.exists(BUFFER_FILE_PATH):
+            os.remove(BUFFER_FILE_PATH)
diff --git a/tests/explorer/runner_pool_test.py b/tests/explorer/runner_pool_test.py
index 285961dc37..eaee55b40a 100644
--- a/tests/explorer/runner_pool_test.py
+++ b/tests/explorer/runner_pool_test.py
@@ -106,6 +106,7 @@ def setUp(self):
             name="test",
             storage_type=StorageType.QUEUE,
             algorithm_type=AlgorithmType.PPO,
+            path="",
         )
         self.queue = QueueReader(
             self.config.buffer.trainer_input.experience_buffer, self.config.buffer
diff --git a/trinity/buffer/buffer.py b/trinity/buffer/buffer.py
index 32a5fb85a8..69f40a8d70 100644
--- a/trinity/buffer/buffer.py
+++ b/trinity/buffer/buffer.py
@@ -61,5 +61,9 @@ def get_buffer_writer(storage_config: StorageConfig, buffer_config: BufferConfig
         from trinity.buffer.writer.queue_writer import QueueWriter
 
         return QueueWriter(storage_config, buffer_config)
+    elif storage_config.storage_type == StorageType.FILE:
+        from trinity.buffer.writer.file_writer import JSONWriter
+
+        return JSONWriter(storage_config, buffer_config)
     else:
         raise ValueError(f"{storage_config.storage_type} not supported.")
diff --git a/trinity/buffer/queue.py b/trinity/buffer/queue.py
index c6a54650aa..f0ddea46c9 100644
--- a/trinity/buffer/queue.py
+++ b/trinity/buffer/queue.py
@@ -9,6 +9,7 @@
 from trinity.buffer.writer.sql_writer import SQLWriter
 from trinity.common.config import BufferConfig, StorageConfig
 from trinity.common.constants import StorageType
+from trinity.utils.log import get_logger
 
 
 def is_database_url(path: str) -> bool:
@@ -26,25 +27,26 @@ class QueueActor:
     FINISH_MESSAGE = "$FINISH$"
 
     def __init__(self, storage_config: StorageConfig, config: BufferConfig) -> None:
+        self.logger = get_logger(__name__)
         self.config = config
         self.capacity = getattr(config, "capacity", 10000)
         self.queue = asyncio.Queue(self.capacity)
-        if storage_config.path is not None and len(storage_config.path) > 0:
-            if is_database_url(storage_config.path):
-                storage_config.storage_type = StorageType.SQL
-                sql_config = deepcopy(storage_config)
-                sql_config.storage_type = StorageType.SQL
-                sql_config.wrap_in_ray = False
-                self.writer = SQLWriter(sql_config, self.config)
-            elif is_json_file(storage_config.path):
-                storage_config.storage_type = StorageType.FILE
-                json_config = deepcopy(storage_config)
-                json_config.storage_type = StorageType.FILE
-                self.writer = JSONWriter(json_config, self.config)
+        st_config = deepcopy(storage_config)
+        st_config.wrap_in_ray = False
+        if st_config.path is not None:
+            if is_database_url(st_config.path):
+                st_config.storage_type = StorageType.SQL
+                self.writer = SQLWriter(st_config, self.config)
+            elif is_json_file(st_config.path):
+                st_config.storage_type = StorageType.FILE
+                self.writer = JSONWriter(st_config, self.config)
             else:
+                self.logger.warning("Unknown supported storage path: %s", st_config.path)
                 self.writer = None
         else:
-            self.writer = None
+            st_config.storage_type = StorageType.FILE
+            self.writer = JSONWriter(st_config, self.config)
+        self.logger.warning(f"Save experiences in {st_config.path}.")
 
     def length(self) -> int:
         """The length of the queue."""
diff --git a/trinity/buffer/db_wrapper.py b/trinity/buffer/ray_wrapper.py
similarity index 65%
rename from trinity/buffer/db_wrapper.py
rename to trinity/buffer/ray_wrapper.py
index bbf96c176e..9de80f32ab 100644
--- a/trinity/buffer/db_wrapper.py
+++ b/trinity/buffer/ray_wrapper.py
@@ -1,3 +1,5 @@
+import json
+import os
 import time
 from typing import List, Optional
 
@@ -8,9 +10,11 @@
 from sqlalchemy.pool import NullPool
 
 from trinity.buffer.schema import Base, create_dynamic_table
-from trinity.buffer.utils import retry_session
+from trinity.buffer.utils import default_storage_path, retry_session
 from trinity.common.config import BufferConfig, StorageConfig
 from trinity.common.constants import ReadStrategy
+from trinity.common.experience import Experience
+from trinity.common.workflows import Task
 from trinity.utils.log import get_logger
 
 
@@ -27,6 +31,8 @@ class DBWrapper:
 
     def __init__(self, storage_config: StorageConfig, config: BufferConfig) -> None:
         self.logger = get_logger(__name__)
+        if storage_config.path is None:
+            storage_config.path = default_storage_path(storage_config, config)
         self.engine = create_engine(storage_config.path, poolclass=NullPool)
         self.table_model_cls = create_dynamic_table(
             storage_config.algorithm_type, storage_config.name
@@ -106,3 +112,60 @@ def read(
         self.logger.info(f"first prompt_text = {exp_list[0].prompt_text}")
         self.logger.info(f"first response_text = {exp_list[0].response_text}")
         return exp_list
+
+
+class _Encoder(json.JSONEncoder):
+    def default(self, o):
+        if isinstance(o, Experience):
+            return o.to_dict()
+        if isinstance(o, Task):
+            return o.to_dict()
+        return super().default(o)
+
+
+class FileWrapper:
+    """
+    A wrapper of a local jsonl file.
+
+    If `wrap_in_ray` in `StorageConfig` is `True`, this class will be run as
+    a Ray Actor, and provide a remote interface to the local file.
+
+    This wrapper is only for writing, if you want to read from the file, use
+    StorageType.QUEUE instead.
+    """
+
+    def __init__(self, storage_config: StorageConfig, config: BufferConfig) -> None:
+        if storage_config.path is None:
+            storage_config.path = default_storage_path(storage_config, config)
+        ext = os.path.splitext(storage_config.path)[-1]
+        if ext != ".jsonl" and ext != ".json":
+            raise ValueError(
+                f"File path must end with '.json' or '.jsonl', got {storage_config.path}"
+            )
+        self.file = open(storage_config.path, "a", encoding="utf-8")
+        self.encoder = _Encoder(ensure_ascii=False)
+
+    @classmethod
+    def get_wrapper(cls, storage_config: StorageConfig, config: BufferConfig):
+        if storage_config.wrap_in_ray:
+            return (
+                ray.remote(cls)
+                .options(
+                    name=f"json-{storage_config.name}",
+                    get_if_exists=True,
+                )
+                .remote(storage_config, config)
+            )
+        else:
+            return cls(storage_config, config)
+
+    def write(self, data: List) -> None:
+        for item in data:
+            json_str = self.encoder.encode(item)
+            self.file.write(json_str + "\n")
+        self.file.flush()
+
+    def read(self) -> List:
+        raise NotImplementedError(
+            "read() is not implemented for FileWrapper, please use QUEUE instead"
+        )
diff --git a/trinity/buffer/reader/sql_reader.py b/trinity/buffer/reader/sql_reader.py
index eb21c92b95..cc725f842c 100644
--- a/trinity/buffer/reader/sql_reader.py
+++ b/trinity/buffer/reader/sql_reader.py
@@ -5,7 +5,7 @@
 import ray
 
 from trinity.buffer.buffer_reader import BufferReader
-from trinity.buffer.db_wrapper import DBWrapper
+from trinity.buffer.ray_wrapper import DBWrapper
 from trinity.common.config import BufferConfig, StorageConfig
 from trinity.common.constants import ReadStrategy, StorageType
 
diff --git a/trinity/buffer/utils.py b/trinity/buffer/utils.py
index ae5927792a..aa2c0e4849 100644
--- a/trinity/buffer/utils.py
+++ b/trinity/buffer/utils.py
@@ -1,6 +1,9 @@
+import os
 import time
 from contextlib import contextmanager
 
+from trinity.common.config import BufferConfig, StorageConfig
+from trinity.common.constants import StorageType
 from trinity.utils.log import get_logger
 
 logger = get_logger(__name__)
@@ -31,3 +34,18 @@ def retry_session(session_maker, max_retry_times: int, max_retry_interval: float
                 raise e
         finally:
             session.close()
+
+
+def default_storage_path(storage_config: StorageConfig, buffer_config: BufferConfig) -> str:
+    if buffer_config.cache_dir is None:
+        raise ValueError("Please call config.check_and_update() before using.")
+    if storage_config.storage_type == StorageType.SQL:
+        return "sqlite:///" + os.path.join(
+            buffer_config.cache_dir,
+            f"{storage_config.name}.db",
+        )
+    else:
+        return os.path.join(
+            buffer_config.cache_dir,
+            f"{storage_config.name}.jsonl",
+        )
diff --git a/trinity/buffer/writer/file_writer.py b/trinity/buffer/writer/file_writer.py
index b163b86b67..0fc4929ca5 100644
--- a/trinity/buffer/writer/file_writer.py
+++ b/trinity/buffer/writer/file_writer.py
@@ -1,39 +1,27 @@
-import json
-import os
 from typing import List
 
+import ray
+
 from trinity.buffer.buffer_writer import BufferWriter
+from trinity.buffer.ray_wrapper import FileWrapper
 from trinity.common.config import BufferConfig, StorageConfig
 from trinity.common.constants import StorageType
-from trinity.common.experience import Experience
-from trinity.common.workflows import Task
-
-
-class _Encoder(json.JSONEncoder):
-    def default(self, o):
-        if isinstance(o, Experience):
-            return o.to_dict()
-        if isinstance(o, Task):
-            return o.to_dict()
-        return super().default(o)
 
 
 class JSONWriter(BufferWriter):
     def __init__(self, meta: StorageConfig, config: BufferConfig):
         assert meta.storage_type == StorageType.FILE
-        if meta.path is None:
-            raise ValueError("File path cannot be None for RawFileWriter")
-        ext = os.path.splitext(meta.path)[-1]
-        if ext != ".jsonl" and ext != ".json":
-            raise ValueError(f"File path must end with .json or .jsonl, got {meta.path}")
-        self.file = open(meta.path, "a", encoding="utf-8")
-        self.encoder = _Encoder(ensure_ascii=False)
+        self.writer = FileWrapper.get_wrapper(meta, config)
+        self.wrap_in_ray = meta.wrap_in_ray
 
     def write(self, data: List) -> None:
-        for item in data:
-            json_str = self.encoder.encode(item)
-            self.file.write(json_str + "\n")
-        self.file.flush()
+        if self.wrap_in_ray:
+            ray.get(self.writer.write.remote(data))
+        else:
+            self.writer.write(data)
 
     def finish(self):
-        self.file.close()
+        if self.wrap_in_ray:
+            ray.get(self.writer.finish.remote())
+        else:
+            self.writer.finish()
diff --git a/trinity/buffer/writer/sql_writer.py b/trinity/buffer/writer/sql_writer.py
index 113ba5773d..e251792f7c 100644
--- a/trinity/buffer/writer/sql_writer.py
+++ b/trinity/buffer/writer/sql_writer.py
@@ -3,7 +3,7 @@
 import ray
 
 from trinity.buffer.buffer_writer import BufferWriter
-from trinity.buffer.db_wrapper import DBWrapper
+from trinity.buffer.ray_wrapper import DBWrapper
 from trinity.common.config import BufferConfig, StorageConfig
 from trinity.common.constants import StorageType
 
diff --git a/trinity/common/config.py b/trinity/common/config.py
index 3a5d0ff57c..42c54c442a 100644
--- a/trinity/common/config.py
+++ b/trinity/common/config.py
@@ -80,6 +80,9 @@ class StorageConfig:
     # used for StorageType.SQL
     wrap_in_ray: bool = True
 
+    # used for StorageType.QUEUE
+    capacity: int = 10000
+
     # used for rollout tasks
     default_workflow_type: Optional[str] = None
     default_reward_fn_type: Optional[str] = None
@@ -234,6 +237,7 @@ class BufferConfig:
     read_batch_size: int = 1  # automatically set
     tokenizer_path: Optional[str] = None  # automatically set
     pad_token_id: Optional[int] = None  # automatically set
+    cache_dir: Optional[str] = None  # automatically set
 
 
 @dataclass
@@ -366,6 +370,7 @@ def _check_interval(self) -> None:
             self.trainer.save_interval = self.synchronizer.sync_interval
 
     def _check_buffer(self) -> None:  # noqa: C901
+        # TODO: split this function into different buffer read/writer
         # check explorer_input
         if self.mode != "train" and not self.buffer.explorer_input.taskset.path:
             raise ValueError(
@@ -426,6 +431,11 @@ def _check_buffer(self) -> None:  # noqa: C901
                 logger.info(
                     f"Auto set `buffer.trainer_input.experience_buffer` to {self.buffer.trainer_input.experience_buffer}"
                 )
+            elif self.buffer.trainer_input.experience_buffer.storage_type is StorageType.FILE:
+                logger.warning(
+                    "`FILE` storage is not supported to use as experience_buffer in `both` mode, use `QUEUE` instead."
+                )
+                self.buffer.trainer_input.experience_buffer.storage_type = StorageType.QUEUE
         elif self.mode == "train":  # TODO: to be check
             if self.algorithm.algorithm_type.is_dpo():
                 if (
@@ -470,6 +480,15 @@ def _check_buffer(self) -> None:  # noqa: C901
                 logger.warning(f"Failed to get pad token id from model {self.model.model_path}")
                 self.buffer.pad_token_id = 0
         self.buffer.tokenizer_path = self.model.model_path
+        # create buffer.cache_dir at <checkpoint_root_dir>/<project>/<name>/buffer
+        self.buffer.cache_dir = os.path.abspath(os.path.join(self.checkpoint_job_dir, "buffer"))
+        try:
+            os.makedirs(self.buffer.cache_dir, exist_ok=True)
+        except Exception:
+            logger.warning(
+                f"Failed to create buffer dir {self.buffer.cache_dir}, please check "
+                f"your checkpoint directory: {self.checkpoint_job_dir}"
+            )
 
     def check_and_update(self) -> None:  # noqa: C901
         """Check and update the config."""
@@ -532,14 +551,14 @@ def check_and_update(self) -> None:  # noqa: C901
 
         self._check_interval()
 
-        # create a job dir in <checkpoint_job_dir>/monitor
+        # create a job dir in <checkpoint_root_dir>/<project>/<name>/monitor
         self.monitor.cache_dir = os.path.join(self.checkpoint_job_dir, "monitor")
         try:
             os.makedirs(self.monitor.cache_dir, exist_ok=True)
         except Exception:
             logger.warning(
                 f"Failed to create monitor dir {self.monitor.cache_dir}, please check "
-                f"your checkpoint directory: {self.checkpoint_root_dir}"
+                f"your checkpoint directory: {self.checkpoint_job_dir}"
             )
 
         # check buffer